  Magnetic interactions between a planet and its environment are known to lead
to aurorae and shocks in the solar system. The large number of close-in
exoplanets that have been discovered so far triggered a renewed interest in
understanding magnetic interactions in other star-planet systems. Multiple
magnetic effects were then unveiled, such as planet inflation or heating,
planet migration, planetary material escape, and even some modifications of the
host star apparent activity. Our goal here is to lay out the basic physical
principles underlying star- planet magnetic interactions. We first briefly
review the hot exoplanets' population as we know it. We then move to a general
description of star-planet magnetic interactions, and finally focus on the
fundamental concept of Alfv\'en wings and its implication for exosystems.
