Recent progresses in chemotherapies and targeted therapies have improved survival in cancer patients. In this context of better-controlled systemic disease, brain metastases (BM) are emerging as a new challenge for the oncologist. However, BM epidemiology and biology remain largely unclear. Incidence of BM is increasing. This trend could be explained by improvement in the quality of neuro-imaging (MRI) and increased survival. Primary cancers associated with BM patients are mainly: lung, breast, renal, colorectal cancers and melanoma. Prevalence of BM is estimated at 9% although this figure is probably underestimated. Time from initial to BM diagnoses is increasing and BM is occurring more frequently in individuals with advanced-stage disease. Biology of BM remains poorly known. Interactions between circulated tumoral cells (CTC) and blood-brain-barrier (BBB) cells are required. Some cytokines may act as CTC attractants and promote BM formation. BM development also involves several steps (extravasations through non-fenestrated capillaries, local proliferation, neoangiogenesis…), which represent potential therapeutic targets.