The relationship between cell adhesiveness and motility is being studied extensively for its paramount importance in the normal development of an organism and in pathological conditions such as tumour metastasis. Although they have been intensively studied at both the cellular and molecular levels, correlative studies of cell structure and adhesiveness, and the precise determination of cell adhesion to a substratum in living cells have been hampered by the fact that cell adhesion has been very difficult to visualize. Two techniques have emerged recently which have allowed successful visualization of cell adhesion. The most recent one, total internal reflection fluorescence, is technically complicated and thus not widespread and so it will not be dealt with here. The other one is a variant of incident light interferometry of thin layers, known as interference reflection microscopy (IRM).