  Galactic globular clusters are not simple stellar populations. And nothing is
simple in their study, basically because we try to reconstruct chains of events
that occurred at redshift z > 2-3 by observing these objects at z=0, after a
Hubble time. Fortunately, spectroscopy offers a magnifying lens: differences of
tens or hundreds of Myrs between stellar generations are translated into
differences in abundances up to a full dex. I will review the complex pattern
emerging by the combined efforts of different groups, focusing on the chemical
signatures of multiple populations in globular clusters.
