In this book, we consider the design of practical distributed space-time codes and power efficient fading mitigation techniques for wireless relay networks. Furthermore, the performance analysis of the wireless relay networks under different protocols and fading channels are investigated. The formulas for the symbol error rate (SER), outage probability, and diversity order of the investigated schemes are presented in fading channels. Based on these SER expressions, power allocations are also introduced to further improve the performance of these systems. The proposed cooperative schemes are next applied to some practical wireless networks. For instance, several amplify-and-forward cooperative schemes are proposed which consider the residual battery energy, as well as the statistical CSI, for the purpose of lifetime maximization in multi-branch, multihop wireless networks. In addition, new energy-efficient cooperative routing protocols are proposed in multihop wireless networks. In contrast to previous works, the proposed cooperating routings depend only on the statistics of the channels, and are implemented by both the centralized and distributed approaches.