What do we mean by professional? Using the commonly understood meaning, skilled or competent, or main income-generating occupation, it is hard to envisage what a body composition professional is. However, if we consider a research scientist, clinical dietitian, sports coach or human biologist, we immediately recognise that such a profession has associated expectations. There are expectations of conduct, in the way individuals are treated; there are expectations of being capable of executing specified tasks, and expectations concerning how both individuals and tasks are managed. Part of the richness of body composition lies in the diversity of its origins and, although professionalism spans each of its disciplines, there are common principles, but also distinct differences in expectation between the different professions which use body composition measures.