  The recent measurements of internal variations of helium in Galactic and
extragalactic Globular Clusters (GCs) set binding constraints to the models of
formation of Multiple Populations (MPs) in GCs, and gave rise, at the same
time, to crucial questions related with the influence of the environment on MP
formation as well as with the role played by GCs in the early galactic
formation. We present the most recent estimates of helium enrichment in the
main populations of a large sample of Galactic and extragalactic GCs.
