Our understanding of epithelial ovarian cancer has blossomed, and we now recognize that it is a collection of varied histologic and molecularly different malignancies, many of which may not derive from a true ovarian anatomic precursor. High-grade serous ovarian cancer (HGSOC) is a unique type of epithelial cancer. It is characterized by nearly universal mutation in and dysfunction of p53, genomic instability rather than driver mutations, advanced stage at onset, and probable fallopian tube epithelium origin, with a serous tubal in situ carcinoma precursor. Germline deleterious mutations in BRCA1 and BRCA2, as well as other less prevalent genes involved in DNA repair, such as PALB2 and RAD51c, are associated with its carcinogenesis and may predict susceptibility to classes of treatment agents, including DNA-damaging agents and DNA repair inhibitors. Loss of function of these genes is associated with homologous recombination dysfunction (HRD). It is now recognized that there may be HGSOC with wild-type BRCA1 and BRCA2 with an identifiable HRD phenotype. Such HRD tumors also may be more susceptible to certain classes of treatments and may be phenotypically detectable with a composite molecular biomarker that has been shown to be predictive for response to PARP inhibitors. Use of this new knowledge of the anatomic and molecular background of HGSOC has led to the rational design of novel combinations of treatment classes to create an HRD-like cellular environment and thus drive treatment benefits.