The chapter uses the principle according to which difference-making or counterfactual dependence is sufficient for causation to show that there are physical effects of mental causes. If non-reductive physicalism is true, applying the principle is straightforward. The principle also yields higher-level causes that are not mental but might be considered problematic. These causes are best diagnosed as causes that have little explanatory relevance. If dualism is true, applying the principle about causation in order to show the existence of mental causation is less straightforward, but still possible. In order to avail themselves of the principle, dualists need to assume that the laws that connect the mental and physical realms have a special status. Rival approaches according to which mental causation or human agency require the transference of a physical quantity or of a power are in conflict with empirical results. The account of mental causation by counterfactual dependence, by contrast, squares with these results.