An ignition system for an internal combustion engine includes an ignition coil having a plurality of primary coils corresponding respectively to individual cylinders of the internal combustion engine, a basic ignition signal detector for producing basic ignition signals in synchronism with the engine rotation, an ignition control circuit for receiving the basic ignition signals and producing an ignition control signal having a controlled predetermined pulse width, a basic cylinder discriminating signal detector for producing a basic cylinder discriminating signal having a period twice that of the basic ignition signals in synchronism with the engine rotation, a cylinder discriminating signal forming logic circuit for receiving the ignition control signal and the basic cylinder discriminating signal and forming a cylinder discriminating signal by changing-over the basic cylinder discriminating signal in accordance with a state thereof, at a transition point of a waveform of the ignition control signal which corresponds to an ignition time of the engine, and an energization signal forming logic circuit for generating an energization signal which controls the energization of a primary coil of the ignition coil for an engine cylinder corresponding to a logic operation output obtained by performing a logic operation on the cylinder discriminating signal and the ignition control signal. This ignition system extends the controllable range of the ignition signal and improves the operational performance of the engine.