The Drosophila position-specific (PS) integrins are members of the integrin family of cell surface receptors and are thought to be receptors for extracellular matrix components. Each PS integrin consists of an alpha subunit, alpha PS1 or alpha PS2, and a beta PS subunit. Mutations in the beta PS subunit and the alpha PS2 subunit have been characterised and reveal that the PS integrins have an essential role in the adhesion of different cell layers to each other. The PS integrins are especially required for the function of the cell-matrix-cell junctions, where the muscles attach to the epidermis and where one surface of the developing wing adheres to the other. These junctions are similar to vertebrate focal adhesions and hemidesmosomes, which also contain integrins. Integrin-mediated cell to cell adhesion via the extracellular matrix provides a way for tissues to adhere to each other without intermingling of their cells.