Following its launch in February 2016 and subsequent commissioning phase, the Copernicus Sentinel-3A satellite has been systematically measuring our oceans, land, ice and atmosphere. The information feeds a range of practical applications and is used for monitoring and understanding large-scale global dynamics. Sentinel-3A will soon be joined in orbit by its identical twin, Sentinel-3B. Both satellites carry a suite of cutting-edge instruments to supply a new generation of data products, which are particularly useful for marine applications. For example, they monitor ocean-surface temperatures for ocean and weather forecasting services, aquatic biological productivity, ocean pollution and sea-level change. The mission also delivers unique and timely information about changing land cover, vegetation, urban heat islands, and for tracking wildfires. With the two satellites in orbit, global coverage and data delivery will be optimised.