  Since 2002, strong, organized magnetic fields have been firmly detected at
the surfaces of about 10 Galactic O-type stars. In this paper I will review the
characteristics of the inferred fields of individual stars, as well as the
overall population. I will discuss the extension of the 'magnetic desert',
first inferred among the A-type stars, to O stars up to 60 solar masses. I will
discuss the interaction of the winds of the magnetic stars with the fields
above their surfaces, generating complex 'dynamical magnetosphere' structures
detected in optical and UV lines, and in X-ray lines and continuum. Finally, I
will discuss the detection of a small number of variable O stars in the LMC and
SMC that exhibit spectral characteristics analogous to the known Galactic
magnetic stars, and that almost certainly represent the first known examples of
extra-Galactic magnetic stars.
