Louis Kahn, architect of the Salk Institute in LaJolla, said "even a common, ordinary brick wants to be something more than it is". Suppose that were also true of molecules. We know that they can and do aggregate; they give complex structures, and by doing so they acquire new properties--functions that may not be apparent from a study of the individual components. This review is about molecular aggregates of a certain sort, namely, those that assemble and more or less completely surround other molecules. Taking part in this intimacy imparts unique properties to the participants, and new functions emerge from the aggregate as a whole. For the most part, we emphasize self-complementary structures. Their ability to assemble-an expression of the molecule's desire to be something more than it is--results from instructions engineered into the molecules during their creation.