The development of the wireless sensor networks (WSNs) in various applications like Defense, Health,
Environment monitoring, Industry etc. always attract many researchers in this field. WSN is the network
which consists of collection of tiny devices called sensor nodes. Sensor node typically combines wireless
radio transmitter-receiver and limited energy, restricted computational processing capacity and
communication band width. These sensor node sense some physical phenomenon using different
transduces. The current improvement in sensor technology has made possible WSNs that have wide and
varied applications. While selecting the right sensor for application a number of characteristics are
important. This paper provides the basics of WSNs including the node characteristics. It also throws light
on the different routing protocols.