  Spectropolarimetric observations combined with tomographic imaging techniques
have revealed that all pre-main sequence (PMS) stars host multipolar magnetic
fields, ranging from strong and globally axisymmetric with ~>kilo-Gauss dipole
components, to complex and non-axisymmetric with weak dipole components (<~0.1
kG). Many host dominantly octupolar large-scale fields. We argue that the
large-scale magnetic properties of a PMS star are related to its location in
the Hertzsprung-Russell diagram. This conference paper is a synopsis of Gregory
et al. (2012), updated to include the latest results from magnetic mapping
studies of PMS stars.
