Wireless sensor network is a special kind of network that differs from the conventional communication networks in terms of architecture and deployment. Dynamic in nature, the wireless sensor networks have added a new dimension not only to the further exploration in a hard-to-reach environment, but also to the complexity of network management. Wireless sensor networks are emerging very rapidly and have already demanded keen interests from researchers. As a relatively new concept in the world of communication, a number of aspects are being explored by the researchers including routing and security features of the wireless sensor networks. Like any wireless network, power consumption has always been a critical issue for wireless sensor networks. This is also due to the environmental constraint in which the wireless sensor networks are normally deployed. This paper provides an overview of this emerging technology by addressing its architecture, deployment and key issues e. g. energy-efficiency, routing, reliability and security