  Magnetic fields are observed not only in stars, but in galaxies, clusters,
and even high redshift Lyman-alpha systems. In principle, these fields could
play an important role in structure formation and also affect the anisotropies
in the cosmic microwave background radiation (CMB). The study of cosmological
magnetic fields aims not only to quantify these effects on large-scale
structure and the CMB, but also to answer one of the outstanding puzzles of
modern cosmology: when and how do magnetic fields originate? They are either
primordial, i.e. created before the onset of structure formation, or they are
generated during the process of structure formation itself.
