This chapter discusses the major differences between Wireless Body Area Networks (WBANs) and Wireless Sensor Networks (WSNs). It explores the details of WBAN architecture, infrastructure design, various sensor types, node characteristics, and quality of service design issues. The chapter describes WBAN media access control layer design issues and the importance of the Institute of Electrical and Electronics Engineers 802.15.6 standard. It deals with data dissemination strategies in WBANs. The chapter discusses the importance of reliability and dependability mechanisms for WBANs. It provides future directions for WBANs. A typical WBAN network is a network of on-body/in-body computing devices that is used in human-centric monitoring. The in-body network provides communication between implanted devices and a base station. The communication architecture is needed to communicate in and around the body. The routing protocols used in WSNs cannot be directly applied to WBANs because the focus in WSNs is maximizing throughput and minimizing routing overhead, which is more important as compared to conserving energy.