Adhesion molecules are membrane proteins responsible for the complex functions of cell adhesion and cellular recognition and are thus of importance in inflammatory as well as neoplastic diseases. Adhesion molecules seem to play a significant role at each level of the metastatic cascade, including the destruction of normal cell-cell as well as cell-substrate cohesion, the penetration of tumor cells into the vascular system and the further spread into distant organs. In this summary an overview of subtypes, structure and function of the major groups of adhesion molecules is given and their possible role in the development, propagation and metastatic spread of malignancies discussed. Cell adhesion and its defects may be of importance in the behaviour of tumor cells and their spread. A better understanding of their function and possible manipulation of their expression, e.g., by cytokines could provide new therapeutic approaches in clinical oncology.