Wireless sensor networks (WSN) are quickly gaining popularity in both military and civilian applications. However, WSN is especially vulnerable against external and internal attacks due to its particular characteristics. It is necessary to provide WSN with basic security mechanisms and protocols that can guarantee a minimal protection to the services and the information flow. This means the hardware layer needs to be protected against node compromise, the communication channels should meet certain security goals (like confidentiality, integrity and authentication), and the protocols and services of the network must be robust against any possible interference. This book provides a deep overview of the major security issues that any WSN designers have to face, and also gives a comprehensive guide of existing solutions and open problems. The book is targeted for the semi-technical readers (technical managers, graduate students, engineers) as well as the specialists. They will get a clear picture regarding what security challenges they will face and what solutions they could use in the context of wireless sensor networks. They will also benefit from the cutting-edge research topics being presented.