Trust plays a crucial role in cloud environment to offer reliable services to the cloud customers. It is the main reason for the popularity of services among the cloud consumers. To achieve this, trust should be established between cloud service provider and cloud consumer. Trust management is widely used in online services, E-commerce and social networks. This review paper focuses on the compilation of the work done by various researchers on trust estimation of service providers and categories of trust models. An attempt is made to identify the various types of trust, quality of service parameters to be considered for trust evaluation and three trust models namely service level agreement (SLA) based trust , recommendation based trust and reputation based trustamong various trust models as reported in literature. Inthis paper, the prime contribution is aboutvarious trust mechanisms involvingin trust evaluations