Silicate melts are major components of magmatic activity and of its most spectacular expression, volcanic eruptions. The “hidden part” is even more fascinating, as silicate melts are directly involved in matter and heat transfer within the Earth and planets. Silicate glasses, often investigated as a frozen picture of their molten counterparts, are also materials of major importance in technology. Despite the difficulties in rationalizing physical and chemical properties of glasses and melts, due to an incomplete knowledge of their structure, major progress has been made recently in synthetic and natural systems. This issue of Elements reviews the properties of silicate glasses and melts from the molecular to the field scale. It includes insights into their technological applications and describes some recent advances this fast-evolving field.