This chapter draws a genealogy of the word ‘protocol’ and its various meanings. It shows that this word, since its origins, has meant both a material object and the function of certifying the authenticity of something or someone. A typology of the varieties of protocols made of five types is then proposed, which shows that the different items called ‘protocols’ historically appear as alternative expressions of normative power. In order to grasp these expressions and their implications, the ways protocols regulate several spheres of social life are explained in their main features. As will emerge, the ‘essence’ of the function of protocollary devices is basically made of three actions: formalising, standardising, and certifying.