Any definition of social work science must make its philosophy of science manifest. While not the only ones in social work to espouse realism, especially critical realism, the IslandWood Group used key ideas from this school of thought to guide many discussions. The main tenets of scientific realism are described followed by a description of some key features of critical realism. Basic tenets of the realisms include the existence of a mind-independent reality, the existence of the unseen, upward and downward causation, stratified reality, emergence, the embrace of multiple methodologies, and the importance of theory in science. This epistemological and ontological stance differs from positivist and behaviorist approaches. The chapter concludes with a summary of other frameworks—pragmatism, constructionism, and critical theories—that are also relevant to a science of social work.