Passive acoustic monitoring (PAM), now widely used for marine mammal research, is typically conducted using hydrophone arrays towed behind ships, providing real-time data from large areas over short time spans (days to weeks), or using fixed autonomous hydrophones, providing non-real-time data from small areas over long time spans (months to years). In contrast, mobile platforms can supply near-real-time data over spatiotemporal scales large in both space and time. These systems are deployed from a vessel, communicate via satellite with shore stations for navigation and control updates, and report in near-real time upon detecting marine mammal or other sounds of interest. Acoustically-equipped gliders are buoyancy-driven devices that are capable of traversing long distances (hundreds to thousands of kilometers) over weeks to months of autonomous operation. Autonomous floats such as QUEphones drift with currents or park on the seafloor, rising to the surface upon detecting sounds of interest. Robot sailboats such as the Roboat use wind to propel themselves quickly over long distances. All platforms can store large datasets and carry additional sensors (e.g., temperature, salinity, chlorophyll, pH, O2), and are therefore well-suited for investigating oceanographic and ecological questions. Advantages and disadvantages of these platforms for various applications will be discussed.