A scan driver and an organic light emitting display (OLED) for selectively performing progressive scanning and interlaced scanning. The scan driver includes a plurality of scan units. A scan unit generates an odd-number scan signal or an even-number scan signal and includes a flip-flop and a scan signal generator. The scan signal generator performs a logical operation on output signals from the flip-flop and a mode selection signal, and outputs a signal. A logical operation can be performed on the output signal of the scan unit and an impulse signal to form a scan signal and an emission control signal. The OLED, which selectively performs the progressive scanning and the interlaced scanning in response to a mode selection signal, includes an emission driver for outputting an emission control signal and a program driver for outputting a scan signal and a boost signal.