Homologous recombination (HR) is a major chromosome damage repair tool. By eliminating DNA double-strand breaks and other deleterious lesions, HR is indispensable for the maintenance of genome stability.In humans, defects in HR directly lead to cancer. This renewal project focuses on the roles of the tumorsuppressors BRCA1, BARD1, BRCA2, and PALB2 in the HR-mediated repair of damaged chromosomes.Considerable progress has been made during the last funding period, leading to important advances inunderstanding HR mechanism.