The selectins are a family of intercellular adhesion molecules that mediate the attachment of leukocytes to the endothelial lining of blood vessels. Another biological process that may involve selectins is the adhesion of circulating tumour cells to endothelium in cancer metastasis. This review discusses the evidence for the involvement of E-, P- and L-selectin in the metastasis of different tumour types. It is concluded that, with certain reservations and qualifications, selectins can play a role in metastasis. For example, the evidence for the involvement of E-selectin in breast and colon cancer metastasis is very strong. For the other selectins and tumour types the evidence is less convincing and further investigations are required to clarify the situation. Certainly, selectins are not the only mechanism available for tumours to metastasise. In the future, measurement of selectins could be useful prognostically and manipulation of their levels could lead to new cancer therapies.