Actin filaments assemble to form different higher-order structures like bundles, dendritic networks, and gel-like networks. Actin bundles are composed of straight actin filaments generated with the help of formins. Actin-crosslinking proteins such as the dimeric alpha-actinin arrange and join the filaments into a loosely packed network of oppositely oriented actin filaments allowing the insertion of myosin. Another monomeric actin-crosslinking protein, fimbrin, forms closely packed parallel bundles of actin filaments in the same orientation. Actin nucleating proteins Arp2/3 guide actin filaments to attach their minus-ends directly to other actin filaments and arrange them in a dendritic network. In gel-like networks, actin filaments are interlinked through filamin, a flexible actin cross-linking protein with two actin-binding domains. Filamin clamps two adjacent actin filaments perpendicular to one another, forming a loose viscous gel-like network.