Index: binaries/data/config/default.cfg
===================================================================
--- binaries/data/config/default.cfg
+++ binaries/data/config/default.cfg
@@ -382,6 +382,7 @@
 experiencestatusbar = true        ; Show an experience status bar above each selected unit
 respoptooltipsort = 0             ; Sorting players in the resources and population tooltip by value (0 - no sort, -1 - ascending, 1 - descending)
 snaptoedgesdistancethreshold = 15 ; On which distance we don't snap to edges
+disjointcontrolgroups = "true"    ; Whether control groups are disjoint sets or entities can be in multiple control groups at the same time.
 
 [gui.session.minimap]
 blinkduration = 1.7               ; The blink duration while pinging
Index: binaries/data/mods/public/gui/options/options.json
===================================================================
--- binaries/data/mods/public/gui/options/options.json
+++ binaries/data/mods/public/gui/options/options.json
@@ -544,6 +544,24 @@
 				"label": "Diplomacy colors: enemy",
 				"tooltip": "Color of enemies when diplomacy colors are enabled.",
 				"config": "gui.session.diplomacycolors.enemy"
+			},
+			{
+				"type": "dropdown",
+				"label": "Control Groups",
+				"tooltip": "Decide whether units can be part of multiple control groups.",
+				"config": "gui.session.disjointcontrolgroups",
+				"list": [
+					{
+						"value": "true",
+						"label": "Disjoint",
+						"tooltip": "When adding units to a selection, they are removed from other control groups. Use this choice if you want each control group to refer to a distinct army."
+					},
+					{
+						"value": "false",
+						"label": "Overlapping",
+						"tooltip": "Units can be part of multiple control groups. This can be useful to keep control groups for distinct armies and the entire army simultaneously."
+					}
+				]
 			}
 		]
 	}
Index: binaries/data/mods/public/gui/session/selection.js
===================================================================
--- binaries/data/mods/public/gui/session/selection.js
+++ binaries/data/mods/public/gui/session/selection.js
@@ -474,12 +474,18 @@
 		this.groups[i] = new EntityGroups();
 }
 
+/**
+ * Add entities to a group.
+ * @param {string} groupName - The number of the group to add the entities to.
+ * @param {number[]} ents - The entities to add to the group.
+ */
 EntityGroupsContainer.prototype.addEntities = function(groupName, ents)
 {
-	for (let ent of ents)
-		for (let group of this.groups)
-			if (ent in group.ents)
-				group.removeEnt(ent);
+	if (Engine.ConfigDB_GetValue("user", "gui.session.disjointcontrolgroups") == "true")
+		for (let ent of ents)
+			for (let group of this.groups)
+				if (ent in group.ents)
+					group.removeEnt(ent);
 
 	this.groups[groupName].add(ents);
 };