In wireless sensor networks (WSNs), nodes are deployed in sensor fields for monitoring and controlling the physical environments. Node localization is fundamental challenge in wireless sensor networks as without knowing the location of nodes sensed information will have no value. Therefore, it is vital that nodes must know their location. This paper provides a review of basic techniques for localization. The localization algorithms are classified into GPS based or GPS free, Anchor based or Anchor free, Centralized or Distributed and Range based or range free. Paper further discusses limitations of each of the algorithms.