Description: The availability of advanced robotic technologies to the Earth Science community has increased in the last decade. Remotely operated vehicles (ROV) enable spatially extensive scientific investigations underneath sea ice, covering a larger range and longer diving times than divers with significantly lower risks. Here we present our experiences made on various aspects of ROV operations during the last five years in the Arctic and Antarctic sea ice region. A particular requirement for ROV operations under sea ice is the ruggedness of the system and resilience towards the harsh climatic conditions. Temperature sensitive control electronics has to cope with operations in temperatures below 0°C and be protected against weather influence. We describe different modes of ROV deployments directly from the sea ice or the support icebreaker. Working at the underside of the sea ice, with obstacles and investigated objects above the vehicle, several paradigms of ROV operations change as compared to blue water applications. This affects not only the buoyancy trim of several system components, but also the positioning of sensor systems and contingency plans for vehicle recovery. Different solutions are available for precise vehicle navigation in a moving ice relative coordinate system. In the framework of the infrastructure project FRAM (Frontiers in Arctic Marine Monitoring), the Alfred Wegener Institute is in the process of commissioning a new lightweight mobile ROV system for interdisciplinary research underneath sea ice. This new system profits from the acquired experiences and will receive a significantly upgraded suite of scientific sensors, maintaining the rugged and reliable characteristics of the past system. The current scientific focus lies on the investigations of the physical and biological properties of sea ice and their spatial variability on floe scale. While basic intervention capabilities are already available, the system can be extended with advanced manipulation and sampling capabilities in the future.