Collapsing ice shelves and increased iceberg calving reflect the widespread speed up of glaciers in Greenland and Antarctica that, over the last two decades, has tripled the contribution of ice sheets to sea level rise. The rapidity of these changes has come as a surprise, revealing major gaps in our understanding of how ice sheets respond to a changing climate. Increased melting under floating ice shelves and at the edge of marine-terminating glaciers, associated with warming ocean waters, has emerged as a likely trigger for glacier speed up, making ice sheet-ocean interactions a scientific priority underlying efforts to improve predictions of climate change and sea level rise. This lecture focuses on advances in our understanding of glacier/ocean exchanges based on observations made at the edge of Greenland’s massive calving glaciers in iceberg-choked fjords using helicopters, icebreakers, fishing vessels, and autonomous vehicles. Here, melting is caused by intrusions of warm, subtropical waters into the fjords and enhanced by muddy plumes of surface melt released hundreds of meters below sea level.