Although firms increasingly publish sustainability reports, assuring such reports is relatively new. This study reviews the literature of sustainability assurance to evaluate the intellectual development of the field and provide recommendations for future studies. It also demonstrates the role of assurance to enhance the credibility of sustainability reports and corporate reputation. This paper systematically reviews 94 papers obtained from the Scopus database between 1993 and August 2021. Our study shows that there is an increase in the number of studies published in recent years. We also found that some countries have received limited attention, such as the USA. The scant literature examining sustainability assurance in private institutions and non-profit organisations should be reinforced. Likewise, the sustainability research also provides limited evidence on the governance debate. The vast majority of research is not based on theoretical grounds. The need for assurance of sustainability reports not only enhances the reputation but also adds more value to the organisation's planning, monitoring, and accountability. We highlight several new research suggestions that may enhance the understanding of sustainability assurance practices.