DNA damage causes devastating problems for developing organisms. Recent studies reveal that BRCA1 plays essential roles in homologous recombinational repair, non-homologous end joining, and nucleotide excision repair. BRCA1 mediates these functions by interaction with components of the DNA repair machinery and by regulating expression of genes that are involved in these DNA damage repair pathways. Consequently, the absence of BRCA1 results in accumulation of chromosome damage, cell cycle abnormalities and apoptosis, leading to developmental abnormalities and adult tumorigenesis. In this review, we discuss recent advances regarding our understanding of the functions of BRCA1 in DNA damage repair and cellular responses that link development and cancer.