  The presence of magnetic fields at the surfaces of many massive stars has
been suspected for decades, to explain the observed properties and activity of
OB stars. However, very few genuine high-mass stars had been identified as
magnetic before the advent of a new generation of powerful spectropolarimeters
that has resulted in a rapid burst of precise information about the magnetic
properties of massive stars. During this talk, I will briefly review modern
methods used to diagnose magnetic fields of higher-mass stars, and summarize
our current understanding of the magnetic properties of OB stars.
