A Wireless Sensor Network consists of spatially distributed autonomous sensors to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants. Basically, each sensor node comprises sensing, processing, transmission, mobilize, position finding system, and power units. These nodes collect and transmit the information. Under light load the data traffic in the network is light. When an event has been detected, the load becomes heavy and the data traffic also increases. This might lead to congestion. The most predicament issues that happen in WSN is Congestion. There are many sources for congestion. They are buffer overflow, concurrent transmission, packet collision etc. Congestion causes packet loss, which in turn reduces throughput and energy efficiency.Therefore congestion in WSN’s needs to be controlled for high energy-efficiency, to prolong system lifetime, improve fairness, and improve quality of service (QoS) in terms of throughput (or link utilization) and packet loss ratio along with the packet delay.This book basically deals with how to reduce congestion in WSN using priority based approach.