The study of fundamental properties (such as temperatures, radii, masses, and ages) and interior processes (such as convection and angular momentum transport) of stars has implications on a wide variety of topics in astrophysics, ranging from modeling spectral energy distributions of galaxies to understanding exoplanet populations. In this talk I will discuss the current state of the art for constraining fundamental properties of stars, focusing in particular on stellar oscillations (asteroseismology) and eclipsing binary stars, both of which have recently been revolutionized through the continuous high-precision photometry provided by the Kepler space telescope. I will furthermore review the current status of optical long-baseline interferometry as a method to directly measure fundamental properties of stars, and its synergy to the data collected by Kepler. Finally, I will give an outlook on the expected impact of current and upcoming space-based missions such as K2, TESS and Gaia on our understanding of stars and stellar populations in our galaxy.