WSN has become one of the important technologies in the present decade. Energy consumption is the major challenge in the field of wireless sensor network. In WSN, there are some hard problems that cannot be solved in deterministic time. These hard problems can be solved by using optimization techniques. Clustering, routing, node localization, maintenance of the nodes, etc., are some of the hard problems that could be addressed. The main aim of these techniques is to provide the solution within specific time and also to minimize the consumption of the energy thus prolonging the lifetime of the network. This paper clearly describes the application of the different published optimization techniques in the field of WSN.