High-performance instruments at large ground-based telescopes have made integral field spectroscopy (IFS) a powerful tool for the study of extended objects such as galaxies, nebulae, or even larger survey fields on the sky. Here we discuss the capabilities of IFS for the study of resolved stellar populations, using the new method of PSF-fitting crowded field IFS, analogous to the well-established technique of crowded field photometry with image sensors. We review early pioneering work with first generation integral field spectrographs, the breakthrough achieved with the MUSE instrument at the ESO Very Large Telescope, the remarkable progress accomplished with MUSE in the study of globular clusters, and first results on nearby galaxies. We discuss the synergy of integral field spectrographs at 8-10m class telescopes with future facilities such as the Extremely Large Telescope (ELT).