Detailed radiative transfer calculations are essential for accurately interpreting spectra, both in solar and stellar astrophysics. The gold standard in spectral synthesis are 3D NLTE calculations, which take advantage of more realistic 3D model atmospheres and account for non-equilibrium physics (NLTE). Over the last decade, 3D NLTE calculations went from a niche to the mainstream. Solar studies have greatly helped in this transition, in two fundamental ways: by developing numerical schemes to make the 3D NLTE problem computationally tractable, and by using our closest star as a detailed laboratory to constrain atomic data and physical assumptions. The repercussions of 3D NLTE analyses in cool stars are profound. I will review a few results, including the revised solar chemical composition and stellar abundances, and finish with an eye on the future, from advances from large spectroscopic surveys, exoplanets, and stellar chromospheres.