Welcome to the special issue of Empirical Software Engineering on the topic of research ethics. We are excited to bring this crucial topic to the attention of empirical researchers. At this point, however, you are probably asking yourself, why ethics and what does it have to do with my research? We will begin to answer this question in this introduction. The articles, cases and commentaries that follow will further detail the relevance of ethics to empirical software engineering research. By the end of the special issue, we hope to have convinced you of the pivotal role that ethics plays in empirical research. We also hope to have convinced you to ensure that the research you conduct and supervise meets ethical standards. Finally, and probably most importantly, we hope to foster a discussion in the research community about ethics and its application to empirical software engineering research.