In recent decades, educational policy researchers have considered critical policy sociology, mostly known as 'policy sociology', as a useful research methodology for analysing educational policies. However, despite its increasing popularity, policy sociology has been a confusing concept hence it is often used interchangeably with other terms such as policy analysis. In the main, there is a dearth of literature outlining its key underlying assumptions and how this methodology helps policy researchers to analyse social, political and economic issues related to educational policy. By reviewing current body of literature in the field, this paper identifies policy sociology as one of the four major traditions in the policy analysis field. The paper presents six key underlying assumptions of policy sociology -- value based study, political study, historical study, multidisciplinary study, assemblage study, and discourse study -- and discusses how researchers have used policy sociology as a research methodology for analysing educational policies.