Sea levels have not only been rising over the past 25 years, but are accelerating, putting coastal communities at risk. With a coastline of more than 100 000 km, many of Europe’s densely populated coastal zones are vulnerable to coastal flooding. It is vital that the changing height of the sea surface continues to be closely monitored over the coming decades. Copernicus Sentinel-6 is the key mission undertaking this important role until at least 2030.