All observational constraints on the internal rotation of stars consistently point to the existence of a missing ingredient in our modeling of angular momentum transport inside stars. Magnetic fields are one of the most serious candidates to produce this additional transport. The recent seismic detection of magnetic fields in the cores of red giants has opened new avenuesto make progress on this important question. The suppression of non-radial modes in a subclass of red giants and in a main-sequence B star has also been interpreted as the potential consequence of strong internal magnetic fields. In this presentation, I will review the seismic methods that have now been explored to reveal magnetic fields in stellar interiors. I will present the constraints that were obtained on the strengths and topologies of these fields, putting the emphasis on the efforts that are still needed to construct an exhaustive catalog of magnetic red giants. Finally, I will briefly touch on how these measurements compare with the few predictions available so far on magnetic angular momentum transport in stars.