These lectures provide insight in both the observational and theoretical aspects of oscillations in stars and what these oscillations reveal about the internal structures of stars. Over the last decade several dedicated space missions (e.g. CoRoT and Kepler) have provided timeseries data of unprecedented precision and length, that revealed oscillations in tens of thousands of stars. As prior to these observations oscillations were only detected in tens to a few hundred stars these space missions have revolutionised the field. Using these oscillations it is possible to obtain the mean density, and surface gravity of low-mass main-sequence stars, subgiants and red-giant stars (the main focus of this lecture, other stars will be touched upon briefly), and with that the mass and radius of the stars. It is also possible to probe the core of subgiants and red-giant stars, to reveal details of the internal structure of these stars, as well as accurate ages.
Using asteroseismology it is possible to obtain precise stellar parameters which are important for stellar evolution studies, as well as for the determination of precise parameters of exoplanets orbiting oscillating stars, and for studies of the Milky Way (galactic archaeology).