Cell interactions are physical points of contact between adjacent cells. They help hold the cells together and allow transmembrane communication, vital to the coordinated functioning of tissues. Stable cell interactions are found in tissues, such as the endothelium, where they support tissue organization. Conversely, weaker, transient interactions help recruit free-moving cells, like immune cells. These cell interactions materialize through special cell-surface proteins, collectively called cell adhesion molecules or CAMs . Of the four major families of CAMs, the integrin family is involved in a cell’s interaction with the extracellular matrix, whereas the other three families are involved in cell-cell interactions. First are the cadherins, which form stable interactions by binding cadherins expressed on other cells. Second are the selectins. They bind specific carbohydrates on the surface of other cells and form transient interactions. And finally, the immunoglobulin-like proteins belonging to the immunoglobulin superfamily also form transient interactions by binding other similar proteins and integrins on other cells.