This AMEE Guide summarizes fundamentals of a major experimental design option for medical education researchers: the randomised study. Medical education researchers face an overwhelming taxonomy of study design options; given the breadth of information on experimental design, the purpose of this Guide is to offer a resource for medical education researchers wishing to equip themselves with helpful information for when to match a study’s objective and the use of randomised designs. Once a research question has been formulated study design is the cornerstone of the intricate, nested activities of any research project. Researchers negotiate many decisions in the pursuit of choosing an appropriate design approach; failure to do so can undermine a project’s capacity to, for example, sufficiently test a hypothesis or theory. Written as an introduction, this Guide is intended for medical education researchers seeking to build on and synthesise the existing corpus of literature on experimental and quasi-experimental design approaches. While not comprehensive, presented are key concepts alongside relevant examples from the field of health professions education.