The present invention is directed to binding molecules that possess one or more epitope-binding sites specific for an epitope of CD 137 and one or more epitope-binding sites specific for an epitope of a tumor antigen ("TA") (e.g., a "CD137 × TA Binding Molecule"). In one embodiment, such CD137 × TA Binding Molecules will be bispecific molecules, especially bispecific tetravalent diabodies, that are composed of two, three, four or more than four polypeptide chains and possessing two epitope-binding sites each specific for an epitope of CD137 and two epitope-binding sites each specific for an epitope of a TA. Alternatively, such CD137 × TA Binding Molecules will be bispecific molecules, especially bispecific trivalent binding molecules composed of three or more polypeptide chains and possessing one or two epitope-binding sites each specific for an epitope of CD137 and one or two epitope-binding sites each specific for an epitope of a TA. The CD137 × TA Binding Molecules of the invention are capable of simultaneous binding to CD137, and a TA. The invention is directed to pharmaceutical compositions that contain any such CD137 × TA Binding Molecules. The invention is additionally directed to methods for the use of such molecules in the treatment of cancer and other diseases and conditions. The invention also provides novel CD137-binding molecules, and HER2/neu-binding molecules, as well as derivatives thereof and uses thereof.