Today, the role of tax professionals has become an important issue in tax policy due to more complex and ambiguous tax laws. For this reason, the study of the activities of tax professionals is important for two reasons. Firstly, Taxpayers use the services of tax professionals to meet their tax obligations. Secondly, tax professionals, more than taxpayers, experience the issue of tax complexity, since their activity comprises the resolution of different tax problems for their clients. Therefore, the views of tax professionals can play an important role in designing country's tax policy. In this review, we study researches on tax professionals' perceptions of tax complexity and its effects on Tax compliance behavior, as well as discuss various methods for measuring the complexity of tax.