Anomalous monism was famously put forward by Donald Davidson. Three claims lie at its core: the principle of causal interaction; the nomological character of causality; and the anomalism of the mental. Davidson's view has been interpreted in various importantly different ways. This chapter describes the two broad kinds of the interpretations of anomalous monism. The first interpretation of anomalous monism is familiar from the work of Jaegwon Kim and Brian McLaughlin, amongst others. On this interpretation, Davidson claims that mental events have two distinct kinds of properties: mental and physical ones. The second interpretation of anomalous monism differs crucially in that it does not ascribe to Davidson a realist view of properties, but instead takes seriously Davidson's nominalism. The chapter then outlines one objection to each interpretation and argues that a third version of anomalous monism is required. It concludes that this is the best version of anomalous monism.