Volcanoes are true wonders of the planet; they are central to the formation, evolution and sustenance of biological systems; they form some of our deepest and most significant cultural attachments to the land; and they attract large numbers of visitors for their aesthetic appeal. Although the primary focus of the analysis in this Study is on volcanic sites that are inscribed on the World Heritage List under criterion (viii), these defining features of volcanoes mean that States Parties may also consider protection of the volcanic heritage value by listing them under other criteria. This Study also provides advice to States Parties on the application of criterion (viii) specifically to volcanic sites. The advice includes the use of the classification system and features identified in this Study to strengthen the nomination of volcanic sites under criterion (viii). The scope of the study is the World Heritage List, but the analysis in this Volcano Thematic Study also includes properties listed in the UNESCO Global Geoparks Programme and sites listed in the UNESCO Man and the Biosphere Programme (Biosphere Reserves).