Internal Medicine is a basic clinical specialty in Medicine, but due to it's vast field of action it is quite difficult to define. This consensus article analyzes different definitions and proposes a current definition while analyzing several aspects of the specialty along with its strengths and weaknesses. We propose to define Internal Medicine as a clinical specialty devoted to the comprehensive care of adults, from adolescence to senility, particularly the diagnosis and non surgical treatment as well as primary and secondary prevention of their diseases, in hospital or ambulatory settings. We propose to define Internal Medicine as a clinical specialty devoted to the comprehensive care of adults in hospital or ambulatory settings, from adolescence to end of life, in terms of prevention, diagnosis and non-surgical treatments of disease.