Heat shock proteins are emerging as important molecules in the development of cancer and as key targets in cancer therapy. These proteins enhance the growth of cancer cells and protect tumors from treatments such as drugs or surgery. However, new drugs have recently been developed particularly those targeting heat shock protein 90. As heat shock protein 90 functions to stabilize many of the oncogenes and growth promoting proteins in cancer cells, such drugs have broad specificity in many types of cancer cell and offer the possibility of evading the development of resistance through point mutation or use of compensatory pathways. Heat shock proteins have a further property that makes them tempting targets in cancer immunotherapy. These proteins have the ability to induce an inflammatory response when released in tumors and to carry tumor antigens to antigen presenting cells. They have thus become important components of anticancer vaccines. Overall, heat shock proteins are important new targets in molecular cancer therapy and can be approached in a number of contrasting approaches to therapy.