This book gives readers an in-depth analysis of the fundamentals behind designing on-demand medium access control (MAC) protocols for multihop wireless networks, esp. with nodes having multiple antenna technologies. This is the first attempt towards designing and analyzing on-demand, also known as contention-based, MAC protocols for multiple beam smart antennas (MBSA). The book begins with a general introduction of the state-of-art problems and solutions that then forms the basis of this book. The book then introduces mathematical models to analyze MBSA and derive basic MAC fundamentals. The readers are then exposed to step-by-step MAC design for MBSA in wireless ad hoc networks. Once the basic design is completed, advanced concepts such as wireless mesh network architecture, Quality of Service (QoS), interoperability with existing IEEE802.11 standards and co-existence with other antenna technologies, viz., omnidirectional and directional, are introduced. Finally, the book ends with introducing link layer reliable and energy-efficient communication mechanisms for wireless sensor networks.