The chapter highlights the differences between the audit of private and public companies, particularly considering the demand and supply for audits of private companies, and reviews the empirical literature on private company audits. The review is organized around the concept of audit quality and focuses on studies on the auditors' ability to detect misstatements and auditor independence, as well as on audit quality inferred from proxy measures in private company audit settings. As access to credit can be of vital importance for private companies, we further review the literature investigating the effect of audits on the private clients' access to credit, financing costs, and credit ratings. Finally, we review the literature on the auditor choice of private companies. To identify the relevant current literature, we conducted a systematic literature search. The review reveals that the majority of the current empirical literature on private company audits largely deals with issues that have already been addressed for public companies and does not exploit the unique opportunities that the private sector offers, such as lower market concentration, different incentives for auditors, and overall greater flexibility due to less regulation. We therefore call for more ingenuity in the choice of topics and research designs.