Integrins are heterodimeric transmembrane glycoproteins involved in cell-cell and cell-extracellular matrix adhesion. They also participate in cytoskeletal rearrangements, co-regulation of growth factor activities and activation of signal transductions. This review describes experimental approaches that have given new insights into the integrin functions during embryogenesis. Using anti-functional antibodies, peptide inhibitors of integrin-ligand interactions and genetic ablation of integrins results, this review will show that integrins are key molecules during early development of both invertebrates and vertebrates.