With globalization and rapid development in scientific communication, eye cancer research is becoming increasingly global, cross-cultural, and collaborative. This chapter deals with an international multicenter retrospective study design and is based on the experience of our research group conducting studies on ocular adnexal lymphoma in collaboration with six international eye cancer centers. The chapter outlines the benefits of international multicenter registry-based research and guides through the distinct phases of our projects. Further, the chapter discusses the challenges that are posed for the investigator at each phase, including obtaining ethical approvals and funding, forming an international registry database, and collecting data from the participating centers. Lastly, the chapter suggests how to deal with these issues and advance international collaboration in ocular oncology.