It is a Self effort done under the supervision of my Respected Supervisor Dr. A Rehman, to surveyed out all the techniques for Energy harvesting in WSNs. Harvesting Systems are basically subdivided into two types. One in which ambient energy is converted to required electrical energy directly without any storage and the other is where storage of converted energy is required before supplying. So for these sub-systems different energy harvesting techniques are proposed which are Radio Frequency based, solar based, thermal based, flow based from source of ambient environment and from external sources of mechanical based & human based. Flow based are further classified into wind based and hydro based. Each energy harvesting technique’s source has its own capability to harvest energy and can effectively overcome the issues of energy consumption.