Abstract: A modular electronic system is constructed by the interconnection of modules containing individual circuits. Each module includes a set of contact pads disposed at sites which are predesignated for the interconnection of corresponding terminals in the various circuits, which terminals are to be interconnected upon assembly of the system. The contact pads are disposed on the exterior surfaces of the modules and in a predetermined arrangement so that all electric connections can be accomplished unambiguously and only upon proper alignment of the modules. Activation of individual circuits may be delayed until completion of assembly by use of a sensing circuit in each module which determines that assembly has been completed or, alternatively, a displaceable connecting plate mounted on a resilient surface may be employed for springing out of connection when the modules are displaced from each other and making connection for activation of the circuits when the modules are contiguous to each other.