T he importance of comparative medicine and the similarities between diseases in humans and animals are concepts fairly easily understood and accepted by all. Publications in this field aimed at a broad audience are generally well received. The importance of scientific advancement in our own veterinary field is an integral part of our daily activities and is spelled out in the American Veterinary Medical Association’s (AVMA) Veterinarian’s Oath (AVMA Policy 1): Being admitted to the profession of veterinary medicine, I solemnly swear to use my scientific knowledge and skills for the benefit of society through the protection of animal health and welfare, the prevention and relief of animal suffering, the conservation of animal resources, the promotion of public health, and the advancement of medical knowledge. I will practice my profession conscientiously, with dignity, and in keeping with the principles of veterinary medical ethics. I accept as a lifelong obligation the continual improvement of my professional knowledge and competence (emphasis added by the authors). As an extension of these concepts, veterinarians work with their human medical counterparts and others in One Health activities, “the integrative effort of multiple disciplines working locally, nationally, and globally to attain optimal health for people, animals, and the environment” (One Health Initiative, AVMA Policy 2 One Health). With these perspectives in mind, it will come as no surprise that the performance of clinical studies or trials directly for the benefit of animals and/or indirectly for the benefit of humans elicit positive, supportive responses, as should be. However, as with similar studies in humans, ethical aspects need to be addressed to protect both the study subjects and their owners and the study directors. In that context, we will review the laws and regulations pertaining to this field as well as some definitions and practical aspects influencing these activities. The terms clinical trial and clinical study are synonymous (ICH). Clinical trials include participants, whether human or animal, who receive specific therapies according to the research protocol developed by the investigators. Clinical trials may involve comparisons between currently recognized therapies (to determine their relative advantages and disadvantages), between a novel investigational treatment and an existing standard of care treatment, or between an investigational treatment and a placebo control. When a new product or approach is studied, it is not usually known whether it will be helpful, harmful, or no different than available alternatives (including no intervention). The principal purpose of any clinical trial is to provide a conclusive resolution to a clinical problem. Biomedical research, clinical studies, and, ultimately, therapy directed at experimentally induced and spontaneously occurring diseases in animals form the basis for animal models of human and animal disease. Comparative medicine may translate basic science knowledge into applied clinical information (AVMA Policy 3, comparative medicine; see also the link at the University of California at Davis, Veterinary Center for Clinical Trials (UC Davis). The mission of the AVMA includes the improvement of animal and human health; this is one of the fundamental goals of biomedical research. The AVMAhas identified the need for companion animal research: research with specifically targeted deliverables for dogs and cats (with horses and other companion species). There has even been a recent endeavor to create an organization to specifically fund this work: the Institute for Companion Animal and Equine Research (AVMA Policy 4 ICAER). Furthermore, the AVMA supports the notion that veterinary medical research is fundamental and encourages academic institutions to have strong veterinary medical research programs (AVMA Policy 5, vet med research). Additionally, the AVMA supports applying knowledge gained from animals with spontaneously occurring disease to enhance the development of new diagnostic tools, vaccines, and therapies for human beings and animals (AVMA Policy 3, comparative medicine). Although this work would be initiated in the realm of basic science, the Philippe J. R. Baneux, DVM, DipECLAM, is Attending Veterinarian, Director Center for Animal Resources and Education at Cornell University in Ithaca, NY. Mary E. Martin, DVM, MPH, DACLAM is Chief, Veterinary and Educational Services at Cornell University, Center for Animal Resources and Education in Ithaca, NY. Matthew J. Allen, Vet.M.B., PhD, is Associate Professor, Orthopedic Surgery, Department of Veterinary Clinical Sciences, College of Veterinary Medicine at The Ohio State University in OH. Troy M. Hallman,Md, VMD is Director of AnimalWelfare at Office of Regulatory Affairs at the University of Pennsylvania in Philadelphia, PA.