This study provides a guide to accounting research on private firms with an emphasis on the European setting. We start by providing an overview of private firm financial reporting regulation in Europe and indicate how this institutional framework can be used to identify promising research settings that in part generalize beyond the European setting. Next, we discuss the availability of private firm accounting data and the underlying data generating process that involves private firms’ original reports, governmental and private data aggregators, and commercial data providers. We show how this process generates insightful data, but at the same time causes complex sample selection issues that researchers should take into account when assessing prior findings and developing new research projects. Finally, we identify potential areas of future work by reviewing the extant literature along the three main motivations for conducting private firm work: (i) to learn more about private firms per se, (ii) to learn more about what distinguishes private firms from public firms, and (iii) to obtain insights from private firms that generalize across all firms.