diff --git a/stix2/v21/bundle.py b/stix2/v21/bundle.py
index 168771f..574ab48 100644
--- a/stix2/v21/bundle.py
+++ b/stix2/v21/bundle.py
@@ -9,9 +9,8 @@ from ..properties import (
 
 
 class Bundle(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_nuwp4rox8c7r>`__.
     """
 
     _type = 'bundle'
diff --git a/stix2/v21/common.py b/stix2/v21/common.py
index ac8daf1..373a7fc 100644
--- a/stix2/v21/common.py
+++ b/stix2/v21/common.py
@@ -16,9 +16,8 @@ from ..utils import NOW, _get_dict
 
 
 class ExternalReference(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_bajcvqteiard>`__.
     """
 
     _properties = OrderedDict([
@@ -51,9 +50,8 @@ class ExternalReference(_STIXBase):
 
 
 class KillChainPhase(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_i4tjv75ce50h>`__.
     """
 
     _properties = OrderedDict([
@@ -63,9 +61,8 @@ class KillChainPhase(_STIXBase):
 
 
 class GranularMarking(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_robezi5egfdr>`__.
     """
 
     _properties = OrderedDict([
@@ -80,9 +77,8 @@ class GranularMarking(_STIXBase):
 
 
 class LanguageContent(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_nfwr8z9ax2bi>`__.
     """
 
     _type = 'language-content'
@@ -108,9 +104,8 @@ class LanguageContent(_STIXBase):
 
 
 class TLPMarking(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_yd3ar14ekwrs>`__.
     """
 
     _type = 'tlp'
@@ -120,9 +115,8 @@ class TLPMarking(_STIXBase):
 
 
 class StatementMarking(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_3ru8r05saera>`__.
     """
 
     _type = 'statement'
@@ -151,9 +145,8 @@ class MarkingProperty(Property):
 
 
 class MarkingDefinition(_STIXBase, _MarkingsMixin):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_hr5vgqxjk7ns>`__.
     """
 
     _type = 'marking-definition'
diff --git a/stix2/v21/observables.py b/stix2/v21/observables.py
index 88f1ff7..89de0fc 100644
--- a/stix2/v21/observables.py
+++ b/stix2/v21/observables.py
@@ -22,9 +22,8 @@ from .common import GranularMarking
 
 
 class Artifact(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_rqwyxo6gp7cv>`__.
     """
 
     _type = 'artifact'
@@ -52,9 +51,8 @@ class Artifact(_Observable):
 
 
 class AutonomousSystem(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_bxebwa6l91fb>`__.
     """
 
     _type = 'autonomous-system'
@@ -74,9 +72,8 @@ class AutonomousSystem(_Observable):
 
 
 class Directory(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_vhpkn06q7fvl>`__.
     """
 
     _type = 'directory'
@@ -100,9 +97,8 @@ class Directory(_Observable):
 
 
 class DomainName(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_i2zf5h7vnrd9>`__.
     """
 
     _type = 'domain-name'
@@ -121,9 +117,8 @@ class DomainName(_Observable):
 
 
 class EmailAddress(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_am7srelb9c14>`__.
     """
 
     _type = 'email-addr'
@@ -143,9 +138,8 @@ class EmailAddress(_Observable):
 
 
 class EmailMIMEComponent(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_kzv52qqc0xw1>`__.
     """
 
     _properties = OrderedDict([
@@ -161,9 +155,8 @@ class EmailMIMEComponent(_STIXBase):
 
 
 class EmailMessage(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_loz634bn09om>`__.
     """
 
     _type = 'email-message'
@@ -202,9 +195,8 @@ class EmailMessage(_Observable):
 
 
 class ArchiveExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_mm25z9wuw4tr>`__.
     """
 
     _type = 'archive-ext'
@@ -215,9 +207,8 @@ class ArchiveExt(_Extension):
 
 
 class AlternateDataStream(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_nbqgazg6fsma>`__.
     """
 
     _properties = OrderedDict([
@@ -228,9 +219,8 @@ class AlternateDataStream(_STIXBase):
 
 
 class NTFSExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_tb77nk1g3y6f>`__.
     """
 
     _type = 'ntfs-ext'
@@ -241,9 +231,8 @@ class NTFSExt(_Extension):
 
 
 class PDFExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_30hzxqrmkg8w>`__.
     """
 
     _type = 'pdf-ext'
@@ -257,9 +246,8 @@ class PDFExt(_Extension):
 
 
 class RasterImageExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_20mnz0u5ppxr>`__.
     """
 
     _type = 'raster-image-ext'
@@ -272,9 +260,8 @@ class RasterImageExt(_Extension):
 
 
 class WindowsPEOptionalHeaderType(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_wyp5qdc2wugy>`__.
     """
 
     _properties = OrderedDict([
@@ -317,9 +304,8 @@ class WindowsPEOptionalHeaderType(_STIXBase):
 
 
 class WindowsPESection(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_wiqw87xsov3t>`__.
     """
 
     _properties = OrderedDict([
@@ -331,9 +317,8 @@ class WindowsPESection(_STIXBase):
 
 
 class WindowsPEBinaryExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_5f9bgdmj91h5>`__.
     """
 
     _type = 'windows-pebinary-ext'
@@ -354,9 +339,8 @@ class WindowsPEBinaryExt(_Extension):
 
 
 class File(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_vq03pryd7u32>`__.
     """
 
     _type = 'file'
@@ -390,9 +374,8 @@ class File(_Observable):
 
 
 class IPv4Address(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_ta83c412bfsc>`__.
     """
 
     _type = 'ipv4-addr'
@@ -412,9 +395,8 @@ class IPv4Address(_Observable):
 
 
 class IPv6Address(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_f76hsv2pvwwq>`__.
     """
 
     _type = 'ipv6-addr'
@@ -434,9 +416,8 @@ class IPv6Address(_Observable):
 
 
 class MACAddress(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_6lhrrdef8852>`__.
     """
 
     _type = 'mac-addr'
@@ -454,9 +435,8 @@ class MACAddress(_Observable):
 
 
 class Mutex(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_u65ia5eoc7cv>`__.
     """
 
     _type = 'mutex'
@@ -474,9 +454,8 @@ class Mutex(_Observable):
 
 
 class HTTPRequestExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_60k6dn28qicj>`__.
     """
 
     _type = 'http-request-ext'
@@ -493,7 +472,7 @@ class HTTPRequestExt(_Extension):
 class ICMPExt(_Extension):
     # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_3g6wds21zwzl>`__.
     """
 
     _type = 'icmp-ext'
@@ -504,9 +483,8 @@ class ICMPExt(_Extension):
 
 
 class SocketExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_f54f1hripxsg>`__.
     """
 
     _type = 'socket-ext'
@@ -566,9 +544,8 @@ class SocketExt(_Extension):
 
 
 class TCPExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_2z78x4m8ewcw>`__.
     """
 
     _type = 'tcp-ext'
@@ -579,9 +556,8 @@ class TCPExt(_Extension):
 
 
 class NetworkTraffic(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_e5nyr5squmsd>`__.
     """
 
     _type = 'network-traffic'
@@ -635,9 +611,8 @@ class NetworkTraffic(_Observable):
 
 
 class WindowsProcessExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_4wfs4ve800kf>`__.
     """
 
     _type = 'windows-process-ext'
@@ -660,9 +635,8 @@ class WindowsProcessExt(_Extension):
 
 
 class WindowsServiceExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_s2rmoe7djlt>`__.
     """
 
     _type = 'windows-service-ext'
@@ -704,9 +678,8 @@ class WindowsServiceExt(_Extension):
 
 
 class Process(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_ur7snm473t1d>`__.
     """
 
     _type = 'process'
@@ -749,9 +722,8 @@ class Process(_Observable):
 
 
 class Software(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_jru33yeokrmh>`__.
     """
 
     _type = 'software'
@@ -774,9 +746,8 @@ class Software(_Observable):
 
 
 class URL(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_6bsklda6vc0c>`__.
     """
 
     _type = 'url'
@@ -794,9 +765,8 @@ class URL(_Observable):
 
 
 class UNIXAccountExt(_Extension):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_z25gmwyz67kl>`__.
     """
 
     _type = 'unix-account-ext'
@@ -809,9 +779,8 @@ class UNIXAccountExt(_Extension):
 
 
 class UserAccount(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_hah33g4ntxnx>`__.
     """
 
     _type = 'user-account'
@@ -842,9 +811,8 @@ class UserAccount(_Observable):
 
 
 class WindowsRegistryValueType(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_6jiqabgqp2hp>`__.
     """
 
     _type = 'windows-registry-value-type'
@@ -872,9 +840,8 @@ class WindowsRegistryValueType(_STIXBase):
 
 
 class WindowsRegistryKey(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_bdim4of4dl37>`__.
     """
 
     _type = 'windows-registry-key'
@@ -897,9 +864,8 @@ class WindowsRegistryKey(_Observable):
 
 
 class X509V3ExtenstionsType(_STIXBase):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_c1kt4dheb6vz>`__.
     """
 
     _type = 'x509-v3-extensions-type'
@@ -924,9 +890,8 @@ class X509V3ExtenstionsType(_STIXBase):
 
 
 class X509Certificate(_Observable):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_g3kniyun8ykv>`__.
     """
 
     _type = 'x509-certificate'
diff --git a/stix2/v21/sdo.py b/stix2/v21/sdo.py
index f2dc0ea..3253a02 100644
--- a/stix2/v21/sdo.py
+++ b/stix2/v21/sdo.py
@@ -22,9 +22,8 @@ from .common import ExternalReference, GranularMarking, KillChainPhase
 
 
 class AttackPattern(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_4ohsa4pay4h4>`__.
     """
 
     _type = 'attack-pattern'
@@ -50,9 +49,8 @@ class AttackPattern(STIXDomainObject):
 
 
 class Campaign(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_vvysvm8mt434>`__.
     """
 
     _type = 'campaign'
@@ -90,9 +88,8 @@ class Campaign(STIXDomainObject):
 
 
 class CourseOfAction(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_d5yf99f0a230>`__.
     """
 
     _type = 'course-of-action'
@@ -116,9 +113,8 @@ class CourseOfAction(STIXDomainObject):
 
 
 class Grouping(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_9e3uldaqqha2>`__.
     """
 
     _type = 'grouping'
@@ -144,9 +140,8 @@ class Grouping(STIXDomainObject):
 
 
 class Identity(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_ru8fmldl2p6w>`__.
     """
 
     _type = 'identity'
@@ -174,9 +169,8 @@ class Identity(STIXDomainObject):
 
 
 class Indicator(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_wfiae74706sw>`__.
     """
 
     _type = 'indicator'
@@ -234,9 +228,8 @@ class Indicator(STIXDomainObject):
 
 
 class Infrastructure(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_l2alfbbcmfep>`__.
     """
 
     _type = 'infrastructure'
@@ -275,9 +268,8 @@ class Infrastructure(STIXDomainObject):
 
 
 class IntrusionSet(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_ticprjb32bc4>`__.
     """
 
     _type = 'intrusion-set'
@@ -318,9 +310,8 @@ class IntrusionSet(STIXDomainObject):
 
 
 class Location(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_sqez6sri9vtz>`__.
     """
 
     _type = 'location'
@@ -426,9 +417,8 @@ class Location(STIXDomainObject):
 
 
 class Malware(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_gc4ooz6oaz7y>`__.
     """
 
     _type = 'malware'
@@ -479,9 +469,8 @@ class Malware(STIXDomainObject):
 
 
 class MalwareAnalysis(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_dw67pa20zss5>`__.
     """
 
     _type = 'malware-analysis'
@@ -524,9 +513,8 @@ class MalwareAnalysis(STIXDomainObject):
 
 
 class Note(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_hr77jvcbs9jk>`__.
     """
 
     _type = 'note'
@@ -552,9 +540,8 @@ class Note(STIXDomainObject):
 
 
 class ObservedData(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_h1590esrzg5f>`__.
     """
 
     _type = 'observed-data'
@@ -608,9 +595,8 @@ class ObservedData(STIXDomainObject):
 
 
 class Opinion(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_sr2hswmu5t1>`__.
     """
 
     _type = 'opinion'
@@ -646,9 +632,8 @@ class Opinion(STIXDomainObject):
 
 
 class Report(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_ha4fpad0r9pf>`__.
     """
 
     _type = 'report'
@@ -675,9 +660,8 @@ class Report(STIXDomainObject):
 
 
 class ThreatActor(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_2wowmlcbkqst>`__.
     """
 
     _type = 'threat-actor'
@@ -722,9 +706,8 @@ class ThreatActor(STIXDomainObject):
 
 
 class Tool(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_m21z3a1f3lou>`__.
     """
 
     _type = 'tool'
@@ -752,9 +735,8 @@ class Tool(STIXDomainObject):
 
 
 class Vulnerability(STIXDomainObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_d9f0iay06wtx>`__.
     """
 
     _type = 'vulnerability'
diff --git a/stix2/v21/sro.py b/stix2/v21/sro.py
index 059bb66..30320b3 100644
--- a/stix2/v21/sro.py
+++ b/stix2/v21/sro.py
@@ -12,9 +12,8 @@ from .common import ExternalReference, GranularMarking
 
 
 class Relationship(STIXRelationshipObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_al0fb8fcd9e7>`__.
     """
 
     _invalid_source_target_types = ['bundle', 'language-content', 'marking-definition', 'relationship', 'sighting']
@@ -69,9 +68,8 @@ class Relationship(STIXRelationshipObject):
 
 
 class Sighting(STIXRelationshipObject):
-    # TODO: Add link
     """For more detailed information on this object's properties, see
-    `the STIX 2.1 specification <link here>`__.
+    `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs01/stix-v2.1-cs01.html#_7p0n81ikux8f>`__.
     """
 
     _type = 'sighting'