This paper provides the first mixed methods theory of causation. According to the theory, the researcher must carefully construct a causal mosaic for each research study, articulating what is causally relevant given his/her research questions, purposes, method(s), methodology(ies), paradigms(s), and resources. To engage in this "mixed methods" process the researcher must understand the multiple dimensions of causality, the multiple philosophical and scientific theories of causation, the quantitative approach to causation, and the qualitative approach to causation. The resulting integrative theory is pluralistic, and includes 11 propositions to guide mixed methods researchers addressing causation. The first proposition states "both quantitative and qualitative approaches to causation are important for a fully defensible social science." The remaining propositions are included in the paper.