Breast cancer is the most prevalent cancer in women worldwide, contributing to 14% of all new cancer cases and 6.8% of all cancer deaths in 2014. A new area of cancer research has arisen from the discovery of cancer cells with stem cell-like properties in several tumor types including the colon, head and breast. Cancer stem cells, which are undifferentiated cells, have the ability of self-renewal, self-replication and differentiating into malignant daughter cells. Breast tumors containing breast cancer stem cells have increased resistance to chemo- and radiotherapy, a higher relapse rate and increased susceptibility to metastasis. Potential targets for the treatment of chemoresistance include signaling pathways of breast cancer stem cells such as the β-catenin-, Notch and Hedgehog pathways. Chemoresistance of these breast cancer stem cells potentially elucidates failure to achieve complete remission post-therapy, and, thus, relapses of breast cancer. By unraveling the mechanism behind the chemotherapeutic resistance of breast cancer stem cells, researchers could develop more efficient treatment strategies towards breast cancer.