Wireless Sensor Networks (WSNs) are currently emerging as one of the most disruptive technologies enabling and supporting next generation ubiquitous and pervasive computing scenarios. In particular, Wireless Body Sensor Networks (WBSNs) are conveying notable attention as their real-world applications aim at improving the quality of human beings life by enabling continuous and real-time non-invasive assistance at low cost and effectively supporting emergency response scenarios. The aim of this chapter is twofold: (i) to provide an overview on WSN technology and (ii) to promote the agent-based model for programming WSNs. In particular, a high-level programming approach based on the agent-oriented model to flexibly design and efficiently implement WBSNs applications is proposed. The approach is contextualized in the emergency response application domain and is exemplified through a case study concerning a real-time human activity monitoring system which is developed through MAPS (Mobile Agent Platform for Sun SPOT), a Java-based framework for Sun SPOT wireless sensors.