The emergence of wireless sensor networks (WSNs) open the way with a multitude of fields of research constituting the privileged seats of their deployment. WSNs consist of small nodes with sensing, computation, and wireless communication capabilities and expected to play an essential role in the upcoming age of pervasive computing. Due to their constraints in computation, memory, power resources, and its deployment in unattended and hostile environments, individual sensors are vulnerable to security compromise and susceptible to physical capture. Furthermore using wireless communications makes security a challenge in these networks. As a result, security must be an important factor to have in mind when designing WSNs. In this book, we present a study of wireless sensor networks, security problem in these networks, we present also a state-of-the-art of key management protocols, as consequence we propose a new protocol for key management.