Considering both the clinical and molecular heterogeneity of breast cancers, one can easily conceive that all tumours are not equally sensitive to the different chemotherapy agents or regimens used. Thus, the identification of predictive markers of chemosensitivity should be considered as a research priority and we analyse here this question in two parts: (1) identification of predictive markers of general chemosensitivity, which means that a tumour is sensitive to any chemotherapy; (2) identification of predictive markers of specific chemotherapy which means that a tumour is sensitive to a specific cytostatic class or to a specific regimen. We will address these two aspects and will summarise ongoing trials and recently published data. These studies suggest the predictive value of biological markers either considered as single molecular markers (hormone receptors, HER2, TOPO2alpha, p53) or as multiple markers combined in so-called "signatures".