This book discusses fundamental security issues in wireless sensor networks, techniques for the protection of such networks, as well as results from recent studies in wireless sensor network security. It contains example applications for target tracking, scientific exploration and data acquisition in hazardous environments, and includes a fairly new study on capabilities of mu-TESLA, a broadcast authentication technique for wireless sensor networks. The book assists both professionals and students to understand background knowledge in wireless sensor network security and prepare them for producing research in this domain.