In this talk, we propose to give a review on the state-of-the-art of the modeling of the dynamics of rotating magnetic stars and of their interactions with their systems, particularly with the orbiting exoplanets. First, we will focus on magnetism and stellar activity across the H-R diagram and on recent advances for our understanding of fossil and dynamo magnetic fields. Next, we will discuss our current understanding of star-planet interactions and of their potential impact both on the dynamics of the host star and the planets. Finally, we will review which observational signatures wouldl allow us to better constrain models and simulations and the perspectives potentially offered by the LUVOIR in this framework.