This book is intended to present an overview and specific applications of cross-layer optimization and cooperative communications in wireless networks. It consists of three main thrusts. In the first thrust, a cross-layer design approach is taken to study rate control in multi-hop wireless networks. Each flow is treated as a ?leaky-pipe? flow and the rate control is explored through effective network utility maximization (ENUM). The second thrust focuses on efficient data transport in wireless sensor networks, where neighboring sensor nodes are organized into coalitions and cooperative communications can be carried out. Energy efficiency, balancing, and probabilistic coverage and connectivity are investigated in this study. The third thrust is on the comparison between MIMO and SISO configurations, where optimal stopping theory is employed to investigate the optimal neighbor selections in multi-channel networks for both antenna configurations.