The molecular chaperone Hsp90 has emerged as an important target in cancer treatment because of its roles in maintaining transformation and regulating the function of proteins involved in apoptotic, survival and growth pathways. Many Hsp90 inhibitors function by binding to the N-terminal ATP pocket, but the chaperone has many other vulnerable points. Agents that interact with its C-terminus or modify its post-translational status represent additional ways of interfering with chaperone activity. This review will discuss several emerging classes of Hsp90 inhibitors and their modes of action.