The role of the tumor microenvironment (TME) is critical in cancer pathobiology. Of the components of the TME, cancer-associated fibroblasts (CAFs) play a major role. Breast cancer is a typical tumor type, forming abundant tumor stroma, and CAFs are involved in various aspects of breast cancer, including carcinogenesis, tumor progression, invasion, metastasis, inflammation, metabolism, therapy resistance, and prognosis. Various factors, such as growth factors, cytokines, hormones secreted from CAFs, paracrine effects promoted by the extracellular matrix (ECM), and mechanical pressure, are involved in cancer development, and there are various crosstalk and signaling pathways among CAFs, cancer cells, epithelial cells, and the ECM. Recent studies have evaluated the potential of CAFs as therapeutic targets in breast cancer. In this review, we discuss the role of CAFs and their clinical implications.