  The chemical makeup of our solar system is a reflection of Galactic chemical
evolution in the local interstellar medium (ISM) over the past ~9 Ga before the
formation of the solar system. Although the incorporated ISM dust was mostly
destroyed during the solar system formation, a small fraction of the ISM dust,
known as presolar grains, is preserved in pristine extraterrestrial materials
and identified through their exotic isotopic compositions, pointing to their
formation in gas outflows or explosions of ancient stars. Since their stellar
birth at more than 4.6 Ga, presolar grains have borne witness to a diverse
array of astrophysical and cosmochemical processes. In this chapter, I will
review recent progress in utilizing the isotopic and structural compositions of
presolar grains to constrain physical mixing processes and dust formation in
stars, stellar nucleosynthesis, ISM processes, and the origin and evolution of
the solar system.
