Research on internal audits of quality management systems is scarce, and no clear study exists that could guide practitioners in improving the auditing practice and help researchers advance existing knowledge. Thus, the aim of this paper is to review empirical research on internal audits of ISO 9001 to synthesise advice for increasing the value of internal audits and to establish a research agenda. The research method used in this paper is a systematic literature review. The result from a thematic analysis revealed two main causes for why internal audits should be improved, three main areas of what to improve, and three groups of suggestions for how audits can be improved. In conclusion, this review show that earlier research agrees on that internal audits focus too much on compliance and less on improvements, and that auditors should improve their knowledge, skills, and audit planning. The implications of this paper are consolidated in four propositions for future research, focusing the need for (1) more research contributing to both practice and theory, (2) enhanced focus on organisational needs and improvement opportunities, (3) changes in audit planning and auditor skills to enable process-oriented auditing, and (4) how to implement changes in internal auditing.