Much research in human-computer interaction involves working with human participants. This requires careful consideration of the ethics of the situation, for both the participants and the researchers. There are numerous ethical codes and guidelines available for HCI researchers, but these are often formulated at an abstract level and provide little practical guidance. This chapter, after briefly presenting a range of codes and guidelines, discusses the ethics of research with humans and the process of applying for ethical approval by considering the different stages of a typical research study using the concept of an ethical audit. The stages are: recruitment of participants; briefing and obtaining informed consent from participants; participants’ activities during the research; and debriefing participants. There are also additional discussions of protecting the researchers and research without participant knowledge. It is argued that conducting an ethical audit before starting a research study or applying for ethical approval, if required, not only makes the process of applying for ethical approval easier and more meaningful for researchers, but may help them make the research more methodologically sound and effective in its results. Finally, some suggestions for future work in this area are presented. These include developing clearer guidelines for conducting research online, better training for students and new researchers in HCI on ethical issues.