Tracing the s-Process: Spectroscopic Insights into Chemical Abundances in O- and C-rich Evolved Stars

Oxygen and carbon-rich AGB stars - and objects directly polluted by them - are excellent laboratories to investigate the nucleosynthesis and mixing processes occurring during the later phases of the of low- and intermediate-mass star evolution. The determination of the abundances of several s-elements is a key tool for constraining theoretical AGB models. This contribution discusses the main results, recent advances, and current problems on this subject.