The polymerization of laminin into a cell‐associated network—a key step in basement membrane assembly—is mediated by the laminin amino‐terminal (LN) domains at the tips of the three short arms of the laminin αβγ‐heterotrimer. The crystal structure of a laminin α5LN–LE1–2 fragment shows that the LN domain is a β‐jelly roll with several elaborate insertions that is attached like a flower head to the stalk‐like laminin‐type epidermal growth factor‐like tandem. A surface loop that is strictly conserved in the LN domains of all α‐short arms is required for stable ternary association with the β‐ and γ‐short arms in the laminin network.