Abstract
Cloud computing has become an important and popular computing model that supports on demand services. It provides its services on pay-per-use basis. Using resources efficiently by reducing execution time and cost and increasing profit is the main goal of cloud service provider. Therefore, using effective scheduling algorithms is still main issue in cloud computing. There is no combined study of scheduling mechanism in cloud computing which describes its levels, policies, and types. This paper focuses on explaining the levels of scheduling in cloud system and presenting scheduling policies used when executing tasks. Also, it provides brief descriptions about various types of scheduling in cloud computing system.