Fibroblasts are mesenchymal cells which came from the embryonic mesoderm. Human Mammary fibroblasts (HMF) synthesize components of the stromal extracellular matrix of the mammary gland. More importantly, such stromal extracellular matrix regulates the proliferation and differentiation of mammary epithelial cells by influencing their gene expression. In addition, HMF play a role in recruiting macrophages for immune surveillance which, in concert with extracellular matrix turnover and angiogenesis, is related with a supportive mammary microenvironment for tumor cell progression. These results suggest that MF play a stimulatory functional role in breast cancer development and invasion. Human Mammary Fibroblasts provide an invaluable tool for understanding physiological and pathophysiological relevance in mammary function and disease.