Basement membranes are extracellular matrices that coat the basal aspect of epithelial and endothelial cells and surround muscle, fat, and Schwann cells. These matrices, first expressed in early embryogenesis, are self-assembled on competent cell surfaces through binding interactions among laminins, type IV collagens, nidogens, and proteoglycans. They form stabilizing extensions of the plasma membrane that provide cell adhesion and act as solid-phase agonists. Basement membranes play a role in tissue and organ morphogenesis and help maintain function in the adult. Mutations affecting their components are associated with developmental arrest and postnatal diseases. The basement membrane (basal lamina) was first described in muscle as a "membranaceous sheath of the most exquisite delicacy." Microscopists later identified basement membranes in nearly all tissues. In the late 1970s, the discovery of the basement membrane-rich EHS tumor led to the isolation of laminin, type IV collagen, nidogen, and perlecan, enabling the elucidation of their biochemical and cell-interactive properties. Basement membranes are layered cell-adherent extracellular matrices that form part of tissue architecture, contributing to embryonic differentiation and adult function. They are evolutionarily ancient structures, likely appearing when organized communities of animal cells first emerged. These matrices serve as an extension of the plasma membrane, protecting tissues from disruptive physical stresses and providing an interactive interface between cells and their environment. Basement membranes contain laminins, nidogens, type IV collagens, and heparan sulfate proteoglycans. These components are organized into supramolecular assemblies that engage cell surface receptors in a developmentally and tissue-specific manner. The assembly of a functionally active basement membrane depends on binding interactions among the large carbohydrate-modified proteins. Integrins are transmembrane heterodimeric receptors that mediate signaling initiated by ligand binding. They act in a bidirectional fashion and are modulated by the mechanical properties of the cell-ECM interface. Integrins affect actin organization and can provide firm anchorage to the cell through linkages with cytoplasmic proteins to F-actin. Integrin signaling affects gene regulation, cell polarity, migration, proliferation, differentiation, and survival. Dystroglycan is part of a complex that forms a link between laminins, agrins, and perlecan to α-dystroglycan, β-dystroglycan, dystrophin, and F-actin. Dystroglycan plays a crucial role in preserving the sarcolemma in the face of muscle contraction and is important for the development of Schwann cell nodes of Ranvier, brain cortex laminations, and parietal endoderm formation. Laminin polymerization and LN-domain binding are essential for basement membrane assembly. The α1-, α2-, α3B-, and α5-laminins can self-assembleBasement membranes are extracellular matrices that coat the basal aspect of epithelial and endothelial cells and surround muscle, fat, and Schwann cells. These matrices, first expressed in early embryogenesis, are self-assembled on competent cell surfaces through binding interactions among laminins, type IV collagens, nidogens, and proteoglycans. They form stabilizing extensions of the plasma membrane that provide cell adhesion and act as solid-phase agonists. Basement membranes play a role in tissue and organ morphogenesis and help maintain function in the adult. Mutations affecting their components are associated with developmental arrest and postnatal diseases. The basement membrane (basal lamina) was first described in muscle as a "membranaceous sheath of the most exquisite delicacy." Microscopists later identified basement membranes in nearly all tissues. In the late 1970s, the discovery of the basement membrane-rich EHS tumor led to the isolation of laminin, type IV collagen, nidogen, and perlecan, enabling the elucidation of their biochemical and cell-interactive properties. Basement membranes are layered cell-adherent extracellular matrices that form part of tissue architecture, contributing to embryonic differentiation and adult function. They are evolutionarily ancient structures, likely appearing when organized communities of animal cells first emerged. These matrices serve as an extension of the plasma membrane, protecting tissues from disruptive physical stresses and providing an interactive interface between cells and their environment. Basement membranes contain laminins, nidogens, type IV collagens, and heparan sulfate proteoglycans. These components are organized into supramolecular assemblies that engage cell surface receptors in a developmentally and tissue-specific manner. The assembly of a functionally active basement membrane depends on binding interactions among the large carbohydrate-modified proteins. Integrins are transmembrane heterodimeric receptors that mediate signaling initiated by ligand binding. They act in a bidirectional fashion and are modulated by the mechanical properties of the cell-ECM interface. Integrins affect actin organization and can provide firm anchorage to the cell through linkages with cytoplasmic proteins to F-actin. Integrin signaling affects gene regulation, cell polarity, migration, proliferation, differentiation, and survival. Dystroglycan is part of a complex that forms a link between laminins, agrins, and perlecan to α-dystroglycan, β-dystroglycan, dystrophin, and F-actin. Dystroglycan plays a crucial role in preserving the sarcolemma in the face of muscle contraction and is important for the development of Schwann cell nodes of Ranvier, brain cortex laminations, and parietal endoderm formation. Laminin polymerization and LN-domain binding are essential for basement membrane assembly. The α1-, α2-, α3B-, and α5-laminins can self-assemble