Carbon, nitrogen, and oxygen are among the first elements to form in the nucleosynthesis chain and comprise most of the mass of elements heavier than helium. These elements play important roles in stellar interiors as sources of opacity and energy production and thus affect the star’s lifetime, its position in the Hertzsprung-Russell diagram, and its heavy-element yields. The CNO elements give comprehensive information on the galactic and stellar evolution. I will present the ongoing work on CNO abundances in galactic open cluster and field stars and its relationship to the Kepler, CoRoT, Gaia, PLATO, and TESS space mission aims.