Oceanographers have long dreamed of a detailed, 4-D view of the ocean. The last decade has witnessed a revolution in autonomous ocean observing capabilities as new platforms and sensors developed, and rapidly matured. As these systems become fully operational, and integrated with other components of the ocean observing system, oceanographers will move closer to realizing this dream. The new generation of oceanographic platforms has been characterized as “autonomous” because the platforms operate—tracking water masses, recording oceanographic properties, and transmitting data home via satellite telemetry—without a tether to either the seafloor or a ship. Autonomous platforms are diverse in their mechanisms and rates of motion; mission payloads, ranges and durations; and capabilities to change sampling parameters during a mission either by receiving commands from home or by using on-board, decision-making tools. The platforms encompass Lagrangian surface drifters, neutrally buoyant and profiling floats, highly controllable self-propelled AUVs (Autonomous Underwater Vehicles), and underwater gliders that adjust their buoyancy to glide forward through the ocean in a saw-tooth pattern. Each platform genre has its own optimum sampling domain, capability to incorporate sensors, and unique potential to contribute to sustained observation of the ocean, such as the U.S. Integrated Ocean Observing System (IOOS).