There is no single phenotypic trait whose exclusive expression correlates universally with metastatic behaviour. Nevertheless, several lines of evidence point towards adhesive phenomena as mediating some crucial steps in the malignant spread of particular tumour types. These steps include detachment from the primary, invasion of the ECM including include detachment from the primary, invasion of the ECM including structures such as the basement membrane and organ capsules, and lodgement in the vessels of remote organs. Furthermore, there is evidence that adhesive phenomena can contribute at least in part to the selective patterns of spread shown by a variety of tumour cell types. The molecular dissection of the adhesive events involved in these processes has only just begun. It is clear already, however, that several different determinants are likely to be involved and the clinical application of this knowledge is unlikely to be immediate.