Reading the book: from "chemical anomalies" to "standard composition" of
  globular clusters
  It is now commonly accepted that globular clusters (GCs) have undergone a
complex formation and that they host at least two stellar generations. This is
a recent paradigm and is founded on both photometric and spectroscopic
evidence. We concentrate on results based on high-resolution spectroscopy and
on how we moved from single to multiple stellar populations concept for GCs. We
underline that the peculiar chemical composition of GC stars is fundamental in
establishing the multiple populations scenario and briefly outline what can be
learned from observations. Finally, recent observational results on large
samples of stars in different evolutionary phases are discussed.
