Vascular invasion (VI) is an essential step in breast cancer metastasis and the main cause of morbidity and mortality from the disease. Detection of VI in the primary tumour is a marker of metastatic potential. The prognostic value of VI in breast cancer has been known for more than four decades, but its application in clinical practice is still fraught with difficulties due to the limited number of studies conducted on large numbers of well-characterized patients with long-term follow-up. Detection of VI in the primary tumour is currently assessed using sections stained with haematoxylin and eosin, which has some disadvantages. A number of vascular markers have been used to improve detection of VI; however, their sensitivity and specificity, as endothelial markers, vary considerably. In this review we describe the evolution of the prognostic importance of VI and the recent pathomolecular mechanisms that contribute to the ability of breast cancers to invade through vessels, in addition to the types, locations and methods of detection of vascular invasion.