The present invention concerns methods and compositions involving inhibitors and enhancers of RAD51, a protein involved in homologous recombination. In some embodiments, the present invention concerns methods for stimulating homologous recombination, which has a number of significant research and clinical applications. In certain other embodiments, there are methods for protecting cells using a compound that enhances RAD51 activity. Such enhancers may also be employed to prevent or reduce damage to cells that may be caused by DNA damaging agents. In other embodiments, there are methods for sensitizing cells to the effects of DNA damaging agents, which can have particular applications for cancer patients. In some embodiments of the invention, the RAD51 enhancer or inhibitor is a small molecule that directly affects RAD51 activity, such as its ability to promote filament formation.