Chemical compositions of asymptotic giant branch stars - A tool for understanding the evolution of cool stars and stellar systems

A selection of problems concerning the evolution of stars and stellar systems is discussed with the common theme that AGE stars and their compositions are part of the search for solutions. The problems considered include the neutron density at s-processing in galactic AGE stars, the origin of the N-rich subdwarfs, and the self-enrichment of the massive globular cluster omega Cen. The review concludes with a discussion of abundance anomalies in RV Tauri variables (post-AGB stars?) attributable to dust-gas separation.