The emerging wireless technologies target a comprehensive range of new applications that the legacy wireless networks cannot support. On the contrary, low rate, low power data collection applications have been anticipated to have a crucial impact on our understanding of the physical world. Simplified technological versions of wireless networks are being worked upon to support these low rate applications in order to meet the stringent requirements of low energy consumption. In wireless networks, Medium Access Control (MAC) sublayer plays a vital role in satisfying the requirement of varying Quality of Service (QoS). Many MAC solutions have been proposed for these networks. In this book, the feasibility of existing solutions for MAC sublayer are reviewed and analyzed for Wireless Sensor Networks. Then the analysis of MAC protocol for recently emerged low rate, low power IEEE 802.15.4 standard is presented. The impact of packet size and number of nodes on the throughput, success probability and average delay is analyzed with Markov chain and OPNET simulation.