This paper presents a differential detection scheme for transmit diversity using two transmit antennas when neither the transmitter nor the receiver has access to channel state information. The scheme uses equal energy constellations and simple encoding, with low decoding complexity at the receiver. It provides full spatial diversity without requiring channel state side information. The paper reviews a simple transmission scheme assuming coherent detection and introduces a new differential encoding algorithm. The corresponding differential decoding algorithm is also presented. Simulation results show a 3 dB loss compared to coherent detection, which is attributed to the noncoherent detection method. The scheme is effective for quasistatic and nonfrequency-selective channels, but performance may degrade in frequency-selective channels. The paper concludes with a discussion on the limitations and future extensions to more than two transmit antennas.This paper presents a differential detection scheme for transmit diversity using two transmit antennas when neither the transmitter nor the receiver has access to channel state information. The scheme uses equal energy constellations and simple encoding, with low decoding complexity at the receiver. It provides full spatial diversity without requiring channel state side information. The paper reviews a simple transmission scheme assuming coherent detection and introduces a new differential encoding algorithm. The corresponding differential decoding algorithm is also presented. Simulation results show a 3 dB loss compared to coherent detection, which is attributed to the noncoherent detection method. The scheme is effective for quasistatic and nonfrequency-selective channels, but performance may degrade in frequency-selective channels. The paper concludes with a discussion on the limitations and future extensions to more than two transmit antennas.