This paper describes a modular approach to creating soft robotic systems. The basis of these systems is an elastomeric actuation element powered by direct mechanical energy in the form of pressurized fluids. Fluidic elastomer actuators are fast and inexpensive to fabricate and offer safety and adaptability to robotic systems. Arrangements of these units can yield arbitrarily complex motions and achieve various functionalities. Actuation power can be generated on-board by a pneumatic battery, which harnesses the catalyzed chemical decomposition of hydrogen peroxide into oxygen gas, for mobile implementations. The modular nature of these robots enable distributed sensing and computation elements. Composition techniques of such soft robots are defined. Example systems are demonstrated and analyzed.