Chemical abundances of multiple stellar populations in massive globular
  clusters
  Multiple stellar populations in the Milky Way globular clusters manifest
themselves with a large variety. Although chemical abundance variations in
light elements, including He, are ubiquitous, the amount of these variations is
different in different globulars. Stellar populations with distinct Fe, C+N+O
and slow-neutron capture elements have been now detected in some globular
clusters, whose number will likely increase. All these chemical features
correspond to specific photometric patterns. I review the chemical+photometric
features of the multiple stellar populations in globular clusters and discuss
how the interpretation of data is being more and more challenging. Very
excitingly, the origin and evolution of globular clusters is being a complex
puzzle to compose.
