Molecular mimics of Smac are capable of modulating apoptosis through their interaction with cellular IAPs (inhibitor of apoptosis proteins). The mimetics are based on a monomer or dimer of the N-terminal tetrapeptide of IAP-binding proteins, such as Smac/DIABLO, Hid, Grim and Reaper, which interact with a specific surface groove of IAP. Also disclosed are methods of using these peptidomimetics for therapeutic purposes. In various embodiments of the invention the Smac mimetics of the invention are combined with chemotherapeutic agents, including, but not limited to topoisomerase inhibitors, kinase inhibitors, NSAIDs, taxanes and platinum containing compounds use broader language