In the past 15 years, the overwhelming observational evidence of multiple stellar populations in globular clusters (GCs) has challenged the idea that a GC consists of stars born at the same time out of the same material. I will discuss the methods and tools to investigate the different populations of stars in GCs, from the point of view of photometry and high resolution spectroscopy, in an effort to shed light on the mechanisms behind the formation of multiple stellar populations. I will then present and discuss detailed chemical abundances of NGC 2808, one of the most massive GCs in our Galaxy, hosting at least five different stellar populations.