  Asymptotic Giant Branch (AGB) stars are important players in the chemical
evolution modelling of galaxies, because they are major producers of several
chemical elements and excellent tracers of the structure and of the star
formation activity of their parent galaxies. A few examples on the importance
of AGB stars are presented in this review, together with a number of open
problems affecting chemical evolution model predictions related to the element
enrichment by AGB stars: the evolution of $^4$He and Na in globular clusters,
the evolution of $^3$He and the carbon isotopes in the Galactic disk, and the
evolution of N and O in different types of galaxies. The need of homogeneous
and complete sets of yields is emphasized.
