  Magnetic fields are known to reside in many astrophysical objects and are now
believed to be crucially important for the creation of phenomena on a wide
variety of scales. However, the role of the magnetic field in the bodies that
we observe has not always been clear. In certain situations, the importance of
a magnetic field has been over looked on the grounds that the large-scale
magnetic field was believed to be too weak to play and important role in the
dynamics.
  In this article I discuss some of the recent developments concerning magnetic
fields in stars, planets and accretion discs. I choose to emphasise some of the
situations where it has been suggested that weak magnetic fields may play a
more significant role than previously thought. At the end of the article I list
some of the questions to be answered in the future.
