Size is one of the most conspicuous properties of anything occurring in the living or inanimate world. We see around us small and large living and non-living entities; our universe is enormous and size even characterizes our immaterial images of gods and thoughts. We obviously assign those differences in size by comparison, according with the perception of our own size. But, are those differences in size relevant in the natural world? Does size really matter? These questions are far from trivial and are shared by scientific disciplines as diverse as ecology, evolutionary biology, neurobiology and developmental biology, among others.