Microelectromechanical systems (MEMS) are impressively sophisticated, micronscale (and increasingly nanoscale) devices that allow computer-controlled actuation of two- and three-dimensional structures. These devices can be designed using conventional mechanical engineering principles and fabricated by employing lithographic techniques. The choice of materials for these devices leads to excellent mechanical robustness, rapid response to electric signals, and manufacturability on a large scale. Although challenging, it should be possible to further miniaturize these devices to the nanoscale by using new design principles and novel nanostructured inorganic materials. In this review, recent developments that combine polymer gels and polymer brushes as potential power sources for the actuation of micromechanical systems will be explored. These systems are in some ways based on biology, which exploits a very wide range of ‘wet’ polymer chemistry to translate chemical energy into mechanical motion. The most complicated of these biological motors exhibit complex conformational changes in their protein machinery during the actuation cycle and these are beyond the reach of current synthetic methods. However, as will be shown below, there are also far simpler biological actuators that are based on charge repulsion and collapse transitions, and it is precisely those systems that will provide the context for the synthetic actuators that are currently being explored.