The term wireless networking refers to technology that enables two or more computers to communicate using standard network protocols and utilizing radio waves. With the rapid development of wireless networking, wireless sensor networks (WSNs) have been emerged which consist of large amount of small resource constrained devices; called sensors. S-MAC is a medium-access control (MAC) protocol designed for wireless sensor networks, it is different from traditional wireless MACs such as IEEE 802.11 in several ways such as energy conservation and self-configuration. A lot of protocols are designed to reduce energy consumption of the wireless sensor nodes. Periodic listen and sleep protocol, adaptive listen protocol and prolong listen protocol are examples of these protocols. In this book, a new S-MAC protocol named; "prediction S-MAC protocol" is proposed to improve the performance of the previous S-MAC protocols.