Triple-negative breast cancer (TNBC) accounts for 15% of all breast cancers and is associated with poor long-term outcomes compared with other breast cancer subtypes. Because of the lack of approved targeted therapy, at present chemotherapy remains the mainstay of treatment for early and advanced disease. TNBC is enriched for germline BRCA mutation, providing a foundation for the use of this as a biomarker to identify patients suitable for treatment with DNA-damaging agents. Inherited and acquired defects in homologous recombination DNA repair, a phenotype termed "BRCAness," may be present in a large proportion of TNBC cases, making it an attractive selection and response biomarker for DNA-damaging therapy. Triple-negative breast cancer is a diverse entity for which additional subclassifications are needed. Increasing understanding of biologic heterogeneity of TNBC has provided insight into identifying potentially effective systemic therapies, including cytotoxic and targeted agents. Numerous experimental approaches are under way, and several encouraging drug classes, such as immune checkpoint inhibitors, poly(ADP-ribose) polymerase inhibitors, platinum agents, phosphatidylinositol-3-kinase pathway inhibitors, and androgen receptor inhibitors, are being investigated in TNBC. Molecular biomarker-based patient selection in early-phase trials has the potential to accelerate development of effective therapies for this aggressive breast cancer subtype. TNBC is a complex disease, and it is likely that several different targeted approaches will be needed to make meaningful strides in improving the outcomes.