This article explores what it is to explain extremism. Rather than providing yet another explanation of extremism, it takes a bird’s eye point of view at existing explanations of extremism. What is it that scholars are doing in seeking explanations of extremism? This article answers this question by considering four issues. First, exactly what is the explanandum for explanations of extremism, what is it that we seek to explain? Second, what is it to explain extremism rather than describing, interpreting, understanding, or predicting it? Third, how can explanations of extremism be categorized and what does that mean for the extent to which can they be combined? Fourth, what semantics is useful in construing an explanation of extremism? It turns out that most insights equally apply to explanations of related yet distinct phenomena, such as fundamentalism, fanaticism, conspiracy theorizing, and terrorism. The article concludes by providing five concrete guidelines that will help fine-tune and compare various explanations of extremism.