In wireless networks, cooperative relaying is an emerging technique that provides spatial diversity in an alternative way. With the help of relays, the source has more opportunities to transmit its data to the destination; in other words, the increased degrees of freedom due to relays can be utilized to combat channel impairments effectively. Therefore, how to choose the optimal relay among a set of available relays for meeting some requirements naturally becomes a critical issue. Recently, various relay selection schemes being proposed aim at choosing one and the best relay in cooperative wireless networks. Some of them require a lot of channel estimations to achieve full diversity order; some of them, on the other hand, avoid high computational complexity as well as frequent channel estimations, but the diversity order is reduced to 2 only. It is the trade-off between the system performance and complexity. In this thesis, we propose two relay selection schemes which need the partial channel state information (CSI), including instantaneous channel power and distance information, to improve the system performance and reduce the system complexity, compared to the existing work. Simulation results demonstrate that the proposed relay selection schemes can achieve better SER performance than the geographic-based scheme and worse SER performance than the instantaneous channel-gain-based scheme.