Cadherins are a large family of calcium-dependent "cell adhesion molecules". In addition to their structural role, cadherins have a number of important functions in the control of cell growth and differentiation. This paper reviews the biology of cadherins and their role in neoplastic transformation, development of the invasive and metastatic phenotype, effects on tumour morphology and the applications of cadherin immunolabelling in tumour diagnosis. Potential areas of future investigation and diagnostic applications are discussed.