Nonequilibrium transient self-assembly In biology, the constant supply of energy can drive a system to be far from its equilibrium conditions and allow for useful work to be done. In contrast, in most synthetic systems, there is a drive toward lower energy states. Boekhoven et al. made a molecule that can switch between a nonassociating state and an associating state through the addition of a chemical fuel (see the Perspective by Van der Zwagg and Meijer). The lifetime, stiffness, and regenerative behavior of the self-assembled state could be controlled and tuned by the kinetics of fuel conversion. Science , this issue p. 1075 ; see also p. 1056