Final Activity Report Summary - MAGRETHEA (Magnetism, rotation and evolution of Herbig Ae/Be stars) Magnetic fields are important components of the Universe, observed at all scales from clusters of galaxies to asteroids. In order to understand the major role of magnetic fields in the formation, evolution and structure of stars, that we believe they play, we have to learn how they form. While it is pretty well understood how solar-type stars generate their magnetic fields, through a convective dynamo, it is more difficult to understand the origin of strong magnetic fields observed in stars more massive than the sun, the so-called intermediate-mass stars (from 1.5 to 10 times the solar mass). Indeed, these stars do not possess a convective envelope favourable to solar-type magnetic field generation. We believe that the magnetic fields in intermediate-mass stars are remnants from the galactic magnetic fields threading molecular clouds in which stars form. Magnetic fields are observed in star forming regions, and in evolved stars. A convincing proof to the proposed fossil theory is detecting magnetic fields at all ages; especially at very young ages, between their birth and more evolved phases, in which observing clues are missing. This project has been mainly devoted to the detection, and characterisation of magnetic fields in very young intermediate-mass stars, the so-called Herbig Ae/Be stars. For the first time we have detected magnetic fields in a sample of Herbig Ae/Be stars, and we were able to prove that these fields are of fossil origin.