Bifunctional inhibitor molecules and methods for their use in the inhibition of protein--protein interactions are provided. The subject bifunctional inhibitor molecules are conjugates of a target protein ligand and a blocking protein ligand, where these two moieties are optionally joined by a linking group. In the subject methods, an effective amount of the bifunctional inhibitor molecule is administered to a host in which the inhibition of a protein--protein interaction is desired. The bifunctional inhibitor molecule simultaneously binds to its corresponding target and blocking proteins to produce a tripartite complex that inhibits the target protein--protein interaction. The subject methods and compositions find use in a variety of applications, including therapeutic applications.