For WSNs, a theoretical framework is proposed that quantifies the significant gains in network performance due to cooperative diversity. Specifically, theory is presented to model routing behavior and cooperative relay selection, using this information to predict the energy consumption and lifetime of the network.This thesis considers the issue of cooperative diversity in two types of wireless networks, wireless sensor networks (WSNs) and wireless ad hoc networks (WAHNs). Analysis in previous works have shown that cooperative diversity increases energy efficiency in 3- and 4-node networks. The contribution of this thesis is extending the analysis to more realistic network settings.For WAHNs, since forwarding packets for others is not voluntary, a pricing system is proposed to stimulate the use of cooperative diversity in such networks. The goal of the pricing system is to induce forwarding in which all members of the network benefit and in situations where it is intuitively reasonable.