  Besides being a source of energy, light can also cool gases of atoms down to
the lowest temperatures ever measured, where atomic motion almost stops. The
research field of cold atoms has emerged as a multidisciplinary one, highly
relevant, e.g., for precision measurements, quantum gases, simulations of
many-body physics, and atom optics. In this focus article, we present the field
as seen in 2015, and emphasise the fundamental role in its development that has
been played by mastering.
