This chapter looks at some of the definitions suggested by renowned scholars and contrasts them with the existing empirical reality, that is, the various categories of dictionaries actually published. Before the advent of modern computer and information technologies, the hitherto most important technological revolution in lexicography was triggered by the invention of the printing press. This disruptive technology quickly made its way into lexicography with radical consequences for both the typography and format of the dictionary article as explained by Ten Haken. Ten Haken characterises dictionaries as tools, whereas Wiegand defines them as utility tools. A tool is a category formulated at a very high level of abstraction and, as such, it constitutes a hypernym of dictionary. The fact that dictionaries are designed to provide information implies that the criteria of content and form are essential to their definition.