Owing to unique features of their design, cluster randomized trials complicate the interpretation of standard ethics guidelines. The recently published Ottawa statement on the ethical design and conduct of cluster randomized trials provides researchers and research ethics committees with detailed guidance on the design, conduct, and review of cluster trials. The Ottawa statement sets out 15 recommendations, including guidance on the justification of study design, the need for research ethics committee review, the identification of research participants, obtaining informed consent, the role of gatekeepers in protecting cluster interests, the assessment of benefits and harms, and the protection of vulnerable participants.