Abstract: A modular electronic musical keyboard instrument includes a plurality of keyboard modules, a signal bus, a plurality of connecting devices, and a signal port. Each of the keyboard modules includes a module casing, a set of signal switches, and a set of finger keys associated operably and respectively with the signal switches. The signal bus includes a plurality of signal lines, each of which is connected electrically to a corresponding one of the signal switches. The signal bus is divided into a plurality of bus sections, each of which is disposed in the module casing of a respective one of the keyboard modules. Each of the connecting devices connects electrically the bus sections of a corresponding adjacent pair of the keyboard modules when the keyboard modules are disposed side by side to form an elongate keyboard body. The signal port is connected electrically to the signal bus.