  Studies of stellar magnetism at the pre-main sequence phase can provide
important new insights into the detailed physics of the late stages of star
formation, and into the observed properties of main sequence stars. This is
especially true at intermediate stellar masses, where magnetic fields are
strong and globally organised, and therefore most amenable to direct study.
This paper reviews recent high-precision spectropolarimetric observations of
pre-main sequence Herbig Ae/Be stars, which are yielding qualitatively new
information about intermediate-mass stars: the origin and evolution of their
magnetic fields; the role of magnetic fields in generating their spectroscopic
activity and in mediating accretion in their late formative stages; the factors
influencing their rotational angular momentum; and the development and
evolution of chemical peculiarity in their photospheres.
