Wireless Sensor Networks (WSN) since their inception, a decade ago, have grown well in research and implementation. In this work the developments in WSNs are reported in three sub areas of wireless sensor networks that is, wireless sensor node (hardware and software), Communication & Networking issues in WSNs and application areas. WSNs are characterized by huge data hence research work in aggregation & mining is also discussed. Contemporary issues of integration of WSNs with other prevalent networks, sensor enabled smartness and role of artificial intelligence methods is elaborated. Insight into future directions & research avenues in all the above areas is provided.