Abstract: The technical research in the field of computational mechanisms for trust and reputation in virtual societies is a latest discipline oriented to increase the reliability and overall performance of electronic communities.Research in the area of trust and reputation systems has put a lot of effort in developing various trust models. In open multi-agent systems trust and reputation is fundamental to improve cooperation by enabling agents to select good partners. In this paper we provide and discuss existing works on trust and reputation models based on centralized and decentralized approach in the area of Multi Agent virtual societies and highlight the limitations as well.Each model presents specific ideas related to calculation of trust. These different trust models are studied and thus subjected to comparison.Trust models play a vital role in determining how communications take place between various agents.

Keywords: Trust, Reputation, Centralized, Decentralized