Archaeological Open-Air Museums (AOAMs) are well established in the international museum landscape, and today more than 350 of these sites can be counted in Europe alone. These museums differ considerably from one another, and each of them presents specific and unique features. Their identity strongly depends on several occurrences, such as the period in which they were founded, the stakeholders who conceived them (private, public, entrepreneurs, academics, amateurs, et cetera), and the cultural paradigms on which they rely. Given the different circumstances that shape them, it is not easy to draw a prototype of an AOAM, and many typologies of sites can easily follow under this name. Starting from these premises, this contribution intends to introduce the first AOAM's classification, based on two main attributes, such as the chronological periods displayed and the location of the AOAM. The article aims to propose a shared terminology to easily describe the AOAMs and refer to their main characteristics with a short and straightforward formula.