This document summarizes the development of remote sensing for mapping snow cover over several decades. It begins with early snow maps from NOAA satellites in the 1960s with 190km resolution and 7 day frequency. Landsat provided 30m resolution in the 1980s but only every 16 days. MODIS in the 2000s improved to 500m resolution daily. Sentinel-2 since 2015 provides snow maps every 5 days at 20m resolution. The document demonstrates combining Landsat-8 and Sentinel-2 data to produce near-daily snow maps for the Pyrenees over 2015-2016, finding improved accuracy over other datasets. Free snow maps are available online with documentation.