The recognition and safeguarding of agricultural heritage in Europe are new concepts that are gaining attention due to the contribution they make to sustainability. Of the 57 Globally Important Agricultural Heritage Systems (GIAHS) that exist in the world today, only six have been designated in Europe. Through a qualitative analysis of the proposal documents submitted by these six European GIAHS to the Food and Agriculture Organization of the United Nations (FAO) during the designation process, this study provides a comparative characterization of these sites supported by expert assessment. During the first phase, 24 specific sub-criteria were observed based on the five main criteria that a site has to meet in order to demonstrate its global relevance as an agricultural heritage of humanity. The relevance of the resulting sub-criteria was then assessed by a Delphi panel of experts and the validated ones were applied in an assessment of the six European sites. The European GIAHS sites are characterized by the high value of their cultural landscapes’ evolution, modeled by traditional and adaptive agriculture knowledge and practices that are promoted and maintained thanks to organized and committed social organizations. The results of structuring of sub-criteria can facilitate the application of other possible European GIAHS sites.