  The actin cortex is a thin layer of actin, myosin, and actin binding proteins
that underlies the membrane of most animal cells. It is highly dynamic and can
undergo remodelling on time-scales of tens of seconds thanks to protein
turnover and myosin-mediated contractions. The cortex enables cells to resist
external mechanical stresses, controls cell shape, and allows cells to exert
forces on their neighbours. Thus, its mechanical properties are key to its
physiological function. Here, we give an overview of how cortex composition,
structure, and dynamics control cortex mechanics and cell shape. We use mitosis
as an example to illustrate how global and local regulation of cortex mechanics
give rise to a complex series of cell shape changes.
