Mockingbird is a prototype tool for developing interlanguage and distributed applications. It compiles stubs from pairs of interface declarations, allowing existing data types to be reused on both sides of every interface. Other multilanguage stub compilers impose data types on the application, complicating development. Mockingbird supports C/C++, Java, and CORBA IDL, and can be extended to other languages. Its stubs convert types whose structural equivalence would be missed by other tools, because it interacts with the programmer to refine the original declarations. We show that this kind of tool improves programming productivity, and describe, in detail, Mockingbird's design and implementation.