Significant advances have been made in the application of genetics to probe the functions of basement membrane laminins. These studies have shown that different laminin subunits profoundly affect tissue morphogenesis, starting around the time of embryonic implantation and extending through organogenesis and into the postnatal period. Collectively they have revealed common functions that include the induction and maintenance of cell polarity, the establishment of barriers between tissue compartments, the organization of cells into tissues, and the protection of adherent cells from detachment-induced cell death, anoikis. Interpreted in light of what is known about laminin structure and self-assembly and binding activities, these advances have begun to provide insights into mechanisms of action. In this review we focus on the contributions of the laminins in invertebrate and vertebrate tissue morphogenesis.