When applied to the Sun, this science is called helioseismology and has been ongoing for a few decades by now. The solar surface helium abundance was derived very accurately for the first time, which has definitely shown the importance of microscopic diffusion in the solar structure. Helioseismology analyses have also unveiled the solar internal rotational profile, the precise extent of the convective envelope and the location of the helium ionization zone. Despite enormous technical challenges, it was thus tempting to apply similar analyses to stars. From the ground this was only possible for stars close to the Sun such as α Centauri, Procyon, β Virginis... The goal is to detect extremely small light variations (down to 1 ppm) and to extract the frequencies responsible for these brightness fluctuations. This produces a frequency spectrum typical of the star under scrutiny. Oscillation periods vary from a few minutes to several hours depending of the type of star and its evolutionary state. To reach such performances, long observing times devoid of day/night alternations are required. Space is thus the ideal asteroseismic laboratory. By revealing their microvariability, measuring their oscillations at the ppm level, CoRoT has provided a new vision of stars, never reached before by any ground-based observation.