ML modules provide hierarchical namespace management, as well as fine-grained control over the propagation of type information, but they do not allow modules to be broken up into separately compilable, mutually recursive components. Mixin modules facilitate recursive linking of separately compiled components, but they are not hierarchically composable and typically do not support type abstraction. We synthesize the complementary advantages of these two mechanisms in MixML. A MixML module is like an ML structure with some components specified but not defined unifing the ML structure and signature languages into one. MixML seamlessly integrates hierarchical composition, translucent MLstyle data abstraction, and mixin-style recursive linking.Tthe design of MixML is minimalist emphasizing how all the interesting features of the ML module system can be understood simply as stylized uses of a small set of orthogonal underlying constructs, with mixin composition playing a central role.