Geotourism is one of the newest concepts within tourism studies today. The popularity of geotourism has likewise grown rapidly over the past few decades. This rapidly growing popularity and the growing body of research on geotourism create the need for a comprehensive review of existing literature on the subject. The present study aims to systematically review scientific literature on geotourism published over the past two decades by identifying what knowledge has been produced on geotourism in the scientific literature and by analyzing the evolving research trends in geotourism during the same time period. The results reveal that researchers are placing an increasing focus on geotourism. A geographical analysis of the study areas indicates a true global distribution, encompassing studies of 53 countries altogether. Most of the research focusses on identifying, describing, and assessing the geoheritage of the areas in question together with their geotourism potential. The volume of research on these topics is growing at a rapid pace. Other common research topics as regards geotourism include management of geotourism and geoheritage, new geosite/geomorphosite assessment models, together with other methodological approaches. The results further indicate that researchers are less interested in geotourism stakeholders such as tourists and local communities, and that only a very small number of studies examine geotourism in the context of sustainable development. The vast majority of the studies utilize empirical data as the basis of the research or for the testing of proposed models and methodology. The present review identifies a need for a larger body of empirical research focusing on (i) sustainability of geotourism, including actual impacts of geotourism on the geoheritage and on the ecosystems of geotourism areas, (ii) knowledge on effective management of the main challenges of geotourism, as well as (iii) on stakeholders and their complex interrelations, including the effects of geotourism on local communities and their well-being.