Wireless Sensor Network (WSN) requires robust and energy efficient communication protocols to minimize the energy consumption as much as possible that means there is battery limitation. A cluster-based scheme is one proposed solution for this problem but for more energy efficiency, The proposed scheme extends High Energy First clustering(HEF) algorithm and enables multi-hop transmissions among the clusters by incorporating the selection of cooperative sending and receiving nodes. The performance of the proposed system is evaluated in terms of energy efficiency and reliability. In this book, the High Energy First clustering algorithm is chosen as a design reference model, which is proved in this book to be an optimal clustering policy under certain ideal conditions In Wireless Sensor Network, the security is one of the key issues. The security purpose of this book is to give the solution for how to provide sensor authentication in wireless sensor networks and how it can be done by suggested energy efficient way. The Cluster-Based Authentication Protocol (APC) is proposed to complete the innovative hybrid symmetric authentication to answer some of the security problems.