Over the past few decades, comprehensive characterization of the cancer genome has elucidated pathways that drive cancer and mechanisms of resistance to therapy and provided important insights for development of new therapies. These advances have resulted in the development of prognostic and predictive tools for use in clinical settings, which can assist clinicians and patients in making informed decisions about the benefits of established therapies. In early-stage breast cancer, multiparameter genomic assays are now available for decision making about the duration of adjuvant endocrine therapy and the use of adjuvant chemotherapy. Similarly, in metastatic disease, there are multiple commercially available next-generation sequencing options for identifying genetic alterations in tumors that may be targeted with a drug. Although these tools hold great promise for providing precision medicine, it can be difficult for the treating physician to evaluate their clinical utility and appropriately select tools for individual clinical situations. This review summarizes the currently available genomic tools in breast cancer, the data underlying their clinical validity and utility, and how they can be used in conjunction with standard clinicopathologic data for making adjuvant and metastatic treatment decisions.