Judgments of explanatory exclusion are a necessary part of the explanatory practice of any historian or social scientist. In this article, the author argues that all explanatory exclusion results from mutual explanatory incompatibility of some sort. Different types of exclusion arise primarily as a result of the different elements composing "an explanation." Of most philosophical interest are judgments of explanatory exclusion resulting from the incompatibility of explanatory relevance claims. The author demonstrates that an ontic theory of explanation is necessary to make sense of this type of exclusion and in so doing develops an analysis similar to Jaegwon Kims well-known analysis of explanatory exclusion. To conclude, the author demonstrates the differences and connections between Kims analysis and his own. Key Words: explanation social science history exclusion compatibility.