The traditional perspective of globular clusters as simple stellar populations is now overcome. In the last years a lot of observational studies (both spectroscopic and photometric) have revealed the presence of chemical anti-correlation between C,O, Mg and N, Na, and Al, respectively, pointing out to pollution processes and to the existence of multiple stellar generations. In this talk I will illustrate our results on determination of lithium and barium abundances in a large sample of globular cluster stars and their relation with proton-capture elements. General implications on cluster formation and early evolution scenarios will be also discussed.