Red giant stars: from mixed modes to angular momentum

Solar-like oscillations are ubiquitous to low-mass stars from the main-sequence to the red-giant branch as demonstrated by the space-borne missions CoRoT and Kepler . Understanding the physical mechanisms governing their amplitudes as well as their behavior along with the star evolution is a prerequisite for interpreting the wealth of seismic data and for inferring stellar internal structure. In this paper, I discuss our current knowledge of mode amplitudes with particular emphasis on non-radial modes in red giants (hereafter mixed modes). Then, I will show how these modes permit to unveil the rotation of the inner-most layers of low-mass stars and how they put stringent constraints on the redistribution of angular momentum.