This chapter seeks to provide insights into the sustainability and non-financial reporting assurance in the public sector by exploring the concept and trends in this issue, which requires considering the developments for the business sector, where it has its origin. The chapter analyses its relevance for accountability and management purposes in the public sector and the state of the art in the literature. The chapter makes a revision of all the developments in the practice at the international level and contains a comparative analysis of the issue in several European countries.