This thesis argues that the fundamental issues within the mental causation debate are metaphysical ones. Consequently, it is only with metaphysical clarity, that any clarity can be gained in the mental causation debate. In order to provide a successful theory of mental causation one cannot divorce oneself from metaphysics. Neither can one hope to provide a theory of mental causation that is somehow neutral between the various metaphysical systems. Rather, to be plausible, a theory of mental causation must be based within an independently plausible metaphysical framework. I divide the metaphysical issues that are of importance to the mental causation debate into three broad groups. Firstly, what causation is a relation between. Secondly, what the existence and identity conditions for properties are. Thirdly, what the causal relation is. Part One of this thesis is concerned with the first of these issues. The interpretation of the argument from causal over determination, and the possible responses to it, depend upon what causation is a relation between. A belief to the contrary, has led to implausible theories of mental causation and the misrepresentation of those positions within the mental causation debate that are ontologically serious. Part Two is concerned with property analysis. It is suggested that a plausible analysis of properties reveals that the true contenders within the mental causation debate are psychophysical reductionism on the one hand, and interactive mentalism on the other. Part Three is concerned with the causal relation. It is argued that the mental causation debate is affected by what one understands causation to be. In particular, whether a causal closure principle that is strong enough to allow one to advance physicalism can plausibly be advanced, depends upon the theory of causation in which one is embedding psychophysical causation.