This introductory article examines how research on terrorism and violence from the extreme right has evolved over the past two decades by comparing the contents of the present Special Issue with those of a previous Special Issue from 1995. This comparative review is divided into three sections: (1) concepts and definitions; (2) data; and (3) theory. Conceptually, the article finds considerable divergence between scholars in the field, and therefore proposes a definition of extreme-right terrorism and extreme-right violence meant to apply across all contexts and actors. Empirically, the article recognizes the inherent challenge of gathering reliable and comparable data on extremeright violence. At the same time, it finds that considerable advances have been made with regards to generating systematic events data suitable for analysing variation across time and place. The article also outlines some of the most important findings emerging from these new data. Theoretically, the article finds some overlap between the two Special Issues concerning proposed causes of extreme-right terrorism and violence. At the same time, many theories do not speak to each other, or even investigate the same types of outcomes. The article therefore concludes by proposing a conceptual distinction between three distinct types of violent outcomes: (1) violent radicalization, (2) violent events, and (3) aggregate levels of violence. By being more explicit about the types of outcomes one seeks to explain, scholars in this field will hopefully move towards a more unified future research agenda.