This is the standard definition of epidemiology, one with which we are all familiar. The definition, of course, never changes, regardless of where you happen to work or carry out your epidemiological study. Specific facets of the job do change, however, under certain circumstances. For example, when looking at the field known as military epidemiology, we must pay special attention to the phrase “specified populations” which appears in the accompanying definition. In fact, the composition of the military population and the conditions under which this population lives and works is what makes this type of epidemiology so special.