The cytoskeleton is the major mechanical structure of the cell; it is a complex, dynamic
biopolymer network comprising microtubules, actin, and intermediate filaments. Both the
individual filaments and the entire network are not simple elastic solids but are instead highly nonlinear structures. Appreciating the mechanics of biopolymer networks is key to under-
standing the mechanics of cells. Here, we review the mechanical properties of cytoskeletal polymers and discuss the implications for the behavior of cells.