Abstract Global datasets on interstate armed conflict suggest that African states clash with each other rarely and only for short periods. This research note shows that existing datasets paint a misleading picture. In fact, African states fight each other more often and for longer than is commonly thought, but they do so by mutually intervening in each other’s intrastate conflicts. Instead of relying solely on their own armed forces, they support their rival’s armed opposition groups. Such mutual interventions—most prevalent in Africa but also evident in other regions—thus span the boundaries of interstate and intrastate conflict. As a result, they have been largely overlooked by conflict scholars. Our note conceptualizes mutual intervention as a distinct form of interstate conflict, comparing and contrasting it with concepts like proxy war, competitive intervention, and international rivalry. The note then presents the first systematic survey of mutual interventions across the African continent. We identify twenty-three cases between 1960 and 2010 and demonstrate that they typically ended independently of their associated intrastate conflicts. We conclude with a research agenda that involves studying the onset, duration, termination, and consequences of mutual interventions, including collecting data on mutual interventions outside Africa to explore cross-regional differences.