To achieve security in WSN it is important to be able to perform various cryptographic operations, including encryption, authentication and authorization. Keys for these cryptographic operations must be setup by communicating nodes before they can exchange information securely. Key management schemes are mechanisms which are used to establish and distribute various kinds of cryptographic keys in the network, such as individual keys, pairwise keys and group keys. Key management is essential cryptographic primitive upon which other security primitives are built. Most security requirements such as privacy, authenticity, integrity can be addressed by building solid key management framework.In fact, a secure key management scheme is the pre-requisite for the security of these primitives, and thus essential to achieving secure infrastructure in sensor networks. There are three types of key management schemes in wireless sensor networks namely Public key cryptographic, Trusted Server Based Schemes and Key Preistribution. The key predistribution is considered best approach for wireless sensor networks.