Abstract: Compounds having an ansamycin anitibiotic, or other moiety which binds to hsp90, coupled to a targeting moiety which binds specifically to a protein, receptor or marker can provide effective targeted delivery of the ansamycin antibiotic leading to the degradation of proteins and death of the targeted cells. These compositions may have different specificity than the ansamycin alone, allowing for a more specific targeting of the therapy, and can be effective in instances where the ansamycin alone has no effect. Thus, these compounds provide an entirely new class of targeted chemotherapy agents with application, depending on the nature of the targeting moiety, to treatment of a variety of different forms of cancer. Such agents can further be used to promote selective degradation of proteins associated with the pathogenesis of others diseases, including antigens associated with autoimmune disorders and pathogenic proteins associated with Alzheimer's disease.