Popper’s theory of World 3 is often regarded as incongruent with his defense of methodological individualism. This article criticizes this widespread view. Methodological individualism is said to be at odds with three crucial assumptions of the theory of World 3: (a) the impossibility of reducing World 3 to subjective mental states because it exists objectively, (b) the view that the mental functions cannot be explained by assuming that individuals are isolated atoms, and (c) the idea that World 3 has causal power and influences both individual minds and actions. This article demonstrates that the inconsistency thesis stems from a confusion between methodological individualism as understood by Popper and reductionism. The reasons for this confusion are analyzed and clarified. It is argued that two variants of methodological individualism can be distinguished, and that unlike psychologistic individualism, Popper’s nonatomistic individualism is fully consistent with his theory of World 3.