Abstract: Cooperative communication has been recently proposed as a way to improve the performance of wireless communication. However, due to the half duplex constraint, most of the relay networks face a fundamental challenge in terms of multiplexing loss. In this paper, we present an adaptive cooperation via relay selection (ACRS) protocol that improves spectral efficiency. This protocol lets the source transmit most of the time and always allows source transmission to be forwarded only by the best transmitter available (maybe source itself) if needed. ACRS has the feature of adapting the system to the fluctuation of the wireless channel and trying to make a packet transmission finished in just one time slot. The diversity-multiplexing tradeoff (DMT) is used to show a remarkable improvement over previous relaying schemes. Simulation results are presented to verify our analysis.