In this thematic issue we discuss what we really know about the explanations for secessionism. Over the last few decades, an increasing number of new analyses on secessionism have appeared, regarding both its normative and its empirical dimensions. We can distinguish at least three types of research questions that categorise the current analyses of secessionism: normative, explanatory, and pragmatic. Political theorists work mainly on the moral and political right to unilaterally secede, answering questions such as “under what conditions” this right is legitimate and “who” has this moral right (Requejo & Sanjaume-Calvet, 2015; Sanjaume‐Calvet, 2020). Despite the importance of normative theories, these approaches do not provide explanations for secessionism, although most of them are built on implicit explanations of these phenomena. The field of explanatory theories of secession focuses mainly on the individual and/or aggregate preconditions and variables that correlate (or not) with the presence (or absence) of secessionist movements in specific territories. Through our general guiding question—”what do we really know about the explanations for secessionism?”—we try to disentangle the current explanations of secessionism by using empirical analyses, combining comparative politics and case studies. We bring together several different analytical perspectives, from political economy, nationalism, electoral behaviour, and institutional studies. Beyond these empirical perspectives, the issue puts forward some normative implications based on what we know and what we do not know about the existence of secessionist claims.