Conducting polymer actuators were first proposed more than ten years ago. Reported performance has improved dramatically, particularly in the past few years, due to changes in synthesis methods, better characterization and an understanding of the underlying mechanisms. These actuators are able to displace large loads (up to 100x greater than mammalian skeletal muscle), with moderate displacements (typically 2 %), and with power to mass ratios similar to that of muscle, while powered using potentials of no more than a few volts. Unlike electric motors and muscle, these actuators exhibit a catch state, enabling them to maintain force without consuming energy. Despite the impressive performance, commercial applications are at an early stage. One reason is the need to carefully consider the details of the actuator construction, including the thickness and surface area of the polymer, the electrolyte conductivity and geometry, the counter electrode spacing, the shape of the input voltage and the means of electrical contact to the polymer, in designing effective actuators. A set of design guidelines is presented that assist the device designer in determining the optimum actuator configuration. These are derived from extensive characterization and modeling of hexafluorophosphate-doped polypyrrole actuators. The set of design tools helps transform conducting polymer actuators into engineering materials that can be selected and designed for particular applications based on rational criteria. Most of the underlying physical principles used in determining these rules also underlie other conducting polymer actuators, polymer devices such as electrochromic displays, supercapacitors and batteries, carbon nanotube actuators, and electrochemically driven devices that involve volumetric charge storage.