diff --git a/src/ifcopenshell-python/ifcopenshell/api/system/assign_port.py b/src/ifcopenshell-python/ifcopenshell/api/system/assign_port.py
new file mode 100644
index 0000000000..2473301327
--- /dev/null
+++ b/src/ifcopenshell-python/ifcopenshell/api/system/assign_port.py
@@ -0,0 +1,69 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2022 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import ifcopenshell
+import ifcopenshell.api
+
+
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {
+            "element": None,
+            "port": None,
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        if self.file.schema == "IFC2X3":
+            return self.execute_ifc2x3()
+
+        rels = self.settings["element"].IsNestedBy or []
+
+        for rel in rels:
+            if self.settings["port"] in rel.RelatedObjects:
+                return
+
+        if not rels:
+            return self.file.create_entity(
+                "IfcRelNests",
+                GlobalId=ifcopenshell.guid.new(),
+                OwnerHistory=ifcopenshell.api.run("owner.create_owner_history", self.file),
+                RelatedObjects=[self.settings["port"]],
+                RelatingObject=self.settings["element"],
+            )
+
+        rel = rels[0]
+        related_objects = set(rel.RelatedObjects) or set()
+        related_objects.add(self.settings["port"])
+        rel.RelatedObjects = list(related_objects)
+        ifcopenshell.api.run("owner.update_owner_history", self.file, **{"element": rel})
+        return rel
+
+    def execute_ifc2x3(self):
+        for rel in self.settings["element"].HasPorts or []:
+            if rel.RelatingPort == self.settings["port"]:
+                return
+        return self.file.create_entity(
+            "IfcRelConnectsPortToElement",
+            GlobalId=ifcopenshell.guid.new(),
+            OwnerHistory=ifcopenshell.api.run("owner.create_owner_history", self.file),
+            RelatingPort=self.settings["port"],
+            RelatedElement=self.settings["element"],
+        )
diff --git a/src/ifcopenshell-python/ifcopenshell/api/system/unassign_port.py b/src/ifcopenshell-python/ifcopenshell/api/system/unassign_port.py
new file mode 100644
index 0000000000..96b3896729
--- /dev/null
+++ b/src/ifcopenshell-python/ifcopenshell/api/system/unassign_port.py
@@ -0,0 +1,51 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2022 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import ifcopenshell
+import ifcopenshell.api
+
+
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {
+            "element": None,
+            "port": None,
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        if self.file.schema == "IFC2X3":
+            return self.execute_ifc2x3()
+
+        for rel in self.settings["element"].IsNestedBy or []:
+            if self.settings["port"] in rel.RelatedObjects:
+                if len(rel.RelatedObjects) == 1:
+                    self.file.remove(rel)
+                    return
+                related_objects = set(rel.RelatedObjects) or set()
+                related_objects.remove(self.settings["port"])
+                rel.RelatedObjects = list(related_objects)
+                ifcopenshell.api.run("owner.update_owner_history", self.file, **{"element": rel})
+
+    def execute_ifc2x3(self):
+        for rel in self.settings["element"].HasPorts or []:
+            if rel.RelatingPort == self.settings["port"]:
+                self.file.remove(rel)
+                return
diff --git a/src/ifcopenshell-python/test/api/system/test_assign_port.py b/src/ifcopenshell-python/test/api/system/test_assign_port.py
new file mode 100644
index 0000000000..b610d463fa
--- /dev/null
+++ b/src/ifcopenshell-python/test/api/system/test_assign_port.py
@@ -0,0 +1,43 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2022 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import test.bootstrap
+import ifcopenshell.api
+import ifcopenshell.util.system
+
+
+class TestAssignPort(test.bootstrap.IFC4):
+    def test_assigning_a_port_once_only(self):
+        port = self.file.createIfcDistributionPort()
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcChiller")
+        ifcopenshell.api.run("system.assign_port", self.file, element=element, port=port)
+        assert element.IsNestedBy[0].RelatedObjects == (port,)
+        assert ifcopenshell.util.system.get_ports(element) == [port]
+        ifcopenshell.api.run("system.assign_port", self.file, element=element, port=port)
+        assert ifcopenshell.util.system.get_ports(element) == [port]
+
+
+class TestAssignPortIFC2X3(test.bootstrap.IFC2X3):
+    def test_assigning_a_port_once_only(self):
+        port = self.file.createIfcDistributionPort()
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcFlowSegment")
+        ifcopenshell.api.run("system.assign_port", self.file, element=element, port=port)
+        assert element.HasPorts[0].RelatingPort == port
+        assert ifcopenshell.util.system.get_ports(element) == [port]
+        ifcopenshell.api.run("system.assign_port", self.file, element=element, port=port)
+        assert ifcopenshell.util.system.get_ports(element) == [port]
diff --git a/src/ifcopenshell-python/test/api/system/test_unassign_port.py b/src/ifcopenshell-python/test/api/system/test_unassign_port.py
new file mode 100644
index 0000000000..2edafa6c1d
--- /dev/null
+++ b/src/ifcopenshell-python/test/api/system/test_unassign_port.py
@@ -0,0 +1,39 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2022 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import test.bootstrap
+import ifcopenshell.api
+import ifcopenshell.util.system
+
+
+class TestAssignPort(test.bootstrap.IFC4):
+    def test_assigning_a_port_once_only(self):
+        port = self.file.createIfcDistributionPort()
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcChiller")
+        ifcopenshell.api.run("system.assign_port", self.file, element=element, port=port)
+        ifcopenshell.api.run("system.unassign_port", self.file, element=element, port=port)
+        assert ifcopenshell.util.system.get_ports(element) == []
+
+
+class TestAssignPortIFC2X3(test.bootstrap.IFC2X3):
+    def test_assigning_a_port_once_only(self):
+        port = self.file.createIfcDistributionPort()
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcFlowSegment")
+        ifcopenshell.api.run("system.assign_port", self.file, element=element, port=port)
+        ifcopenshell.api.run("system.unassign_port", self.file, element=element, port=port)
+        assert ifcopenshell.util.system.get_ports(element) == []