Laminin is a large trimeric glycoprotein, found in all basement membranes and the extracellular matrix of the developing central nervous system (Timpl 1989, Beck et al. 1990, Tryggvason 1993, Colognato & Yurchenco 2000). It forms extended polymeric networks that contact the cell surface. Laminin can self-assemble even in the absence of other basement membrane components (Yurchenco et al. 1992) suggesting a key developmental role. Laminin polymerization is thought to be driven by attachment of laminin to cell surface receptors, dystroglycan or integrins, and possibly other receptors. Receptor-engaged laminin exceeds the critical concentration for self-assembly (Colognato & Yurchenco 2000). Binding experiments agree with a proposed three-arm interaction model where the short arm laminin amino-terminal (LN) domains interact alpha-beta, alpha-gamma and beta-gamma to form a polygonal network (Yurchenco et al. 1985, Odenthal et al. 2004).