This article provides a general overview of the current state of research on Cassius Dio and focuses on some current trends and issues of debate in the field. The turn of the twenty-first century witnessed a real breakthrough in Dio scholarship, which has greatly advanced in many respects through increasing diversification of research topics, innovative approaches, posing new questions and producing important conceptual generalizations. International projects and wide academic collaborations, above all the Dioneia project (Lire Cassius Dion: cinquante ans après Fergus Millar: bilans et perspectives) and the Cassius Dio Network: Cassius Dio, Between History and Politics, have contributed greatly to this process. This intensive academic activity has resulted in new editions, translations and commentaries of Dio’s Roman History, numerous dissertations and monographs, which make Cassius Dio a much better understood historian than twenty or even five years ago. But there are still not a few issues of controversy and debate, including the historian’s approach to causation, particularly his vision of human nature as a factor of history. An analytical survey of the ongoing studies of that issue shows that Dio is treated as an author who independently elaborated on the themes he dealt with, without being entirely dependent on the interpretative models derived from Thucydides or elsewhere. This supports the status of Dio as a historian with his own voice.