A wireless sensor network (WSN) usually consists of a large number of small, low-cost devices that have limited energy supply, computation, memory, and communication capacities. Recently, WSNs have drawn a lot of attention due to their broad applications in both military and civilian domains. Communication security is essential to the success of WSN applications, especially for those mission-critical applications working in unattended and even hostile environments. However, providing satisfactory security protection in WSNs has ever been a challenging task due to various network & resource constraints and malicious attacks. This motivates extensive research on communication security for WSNs. This book studies communication security in WSNs regarding three important aspects, namely, broadcast/multicast security, data report security, and random key pre-distribution. The latest research results on these topics are discussed in detail. The book will be of interest to researchers in the area of network security and wireless networks. It is also directed towards senior undergraduate and graduate students major in computer networks and information security.