Plug connector modular system comprising at least one plug connector module' (3, 3') and a plug connector modular frame, suitable for fitting into a plug connector housing or a wall aperture and intended for establishing a plug-side plug-in connection with a mating connector, wherein the plug connector modular frame is suitable for receiving a number of plug connector modules (3, 3') and has a cross section which is rectangular in the plane of its frame and has two side parts (11, 12) opposite one another, which respectively have mating latching means for latching of the plug connector modules, wherein the plug connector modular frame is of a rigid and onepart configuration, wherein the plug connector module (3, 3') is suitable for being fixed in the plug connector modular frame, wherein the plug connector module (3, 3') has a substantially cuboidal insulating body with two end faces opposite and parallel to one another, wherein the insulating body has a holding portion, by which it can be securely and stably held perpendicularly to its end faces in the plug connector modular frame, wherein the insulating body also has a deforming portion, which is movable at least in certain regions in relation to the holding portion, whereby the plug connector module (3, 3') can assume on the one hand a locking state and on the other hand an unlocking state, characterized in that, in its unlocking state, the plug connector module (3, 3') can be both removed from the plug connector modular frame and inserted into it, perpendicularly to the plane of the frame, in and counter to the plugging direction, and wherein, in its locking state, the plug connector module (3, 3') can be latched on the plug connector modular frame, and consequently can be fixed in the plug connector modular frame perpendicularly to the plane of the frame. wherein the plug connector modular frame is suitable for receiving a number of plug connector modules (3, 3') and has a cross section which is rectangular in the plane of its frame and has two side parts (11, 12) opposite one another, which respectively have mating latching means for latching of the plug connector modules, wherein the plug connector modular frame is of a rigid and onepart configuration, wherein the plug connector module (3, 3') is suitable for being fixed in the plug connector modular frame, wherein the plug connector module (3, 3') has a substantially cuboidal insulating body with two end faces opposite and parallel to one another, wherein the insulating body has a holding portion, by which it can be securely and stably held perpendicularly to its end faces in the plug connector modular frame, wherein the insulating body also has a deforming portion, which is movable at least in certain regions in relation to the holding portion, whereby the plug connector module (3, 3') can assume on the one hand a locking state and on the other hand an unlocking state, characterized in that, in its unlocking state, the plug connector module (3, 3') can be both removed from the plug connector modular frame and inserted into it, perpendicularly to the plane of the frame, in and counter to the plugging direction, and wherein, in its locking state, the plug connector module (3, 3') can be latched on the plug connector modular frame, and consequently can be fixed in the plug connector modular frame perpendicularly to the plane of the frame.