Cell adhesion plays important roles in the normal functions of cells, contributing to cellular organization and structure, proliferation and survival, and gene expression. During development, cell adhesion is important for the correct movements of cells modeling the embryo. In the adult, appropriate cell adhesion is necessary for numerous physiological processes and can be deranged in many diseases, including cancer. Changes in cell adhesion contribute to the initial migration and invasion of malignant tumor cells, the first steps leading to metastasis. In later steps of metastasis, cell adhesion is vital for the entry of cancer cells into the blood, their survival, and their establishment at distant sites in the body.