Invasion and metastasis of tumor cells is the primary cause for the fatal outcome of cancer diseases. A striking feature of metastatic cells is the considerable flexibility in their adhesive interactions with other cells or components of the extracellular matrix. This review will describe the involvement of specific cell adhesion receptors, extracellular matrix molecules, and cell dissociating cytokines in the metastatic cascade. We will particularly focus on disturbance of intercellular adhesion as a prerequisite for the release of invasive cells from carcinomas. We suggest that cell dissociation in these tumors is accomplished by loss of function or expression of the epithelial cell adhesion molecule E-cadherin, and through the activity of cell motility factors, like scatter factor.