  Magnetic fields are involved in every astrophysical process on every scale:
from planetary and stellar interiors to neutron stars, stellar wind bubbles and
supernova remnants; from the interstellar medium in galactic disks, nuclei,
spiral arms and halos to the intracluster and intergalactic media. They are
involved in essentially every particle acceleration process and are thus
fundamental to non-thermal physics in the Universe. Key questions include the
origin of magnetic fields, their evolution over cosmic time, the amplification
and decay processes that modify their strength, and their impact on other
processes such as star formation and galaxy evolution. Astrophysical plasmas
provide a unique laboratory for testing magnetic dynamo theory. The study of
magnetic fields requires observations that span the wavelength range from radio
through infrared, optical, UV, X-ray, and gamma-ray.
  Canada has an extremely strong record of research in cosmic magnetism, and
has a significant leadership role in several ongoing and upcoming global
programs. This white paper will review the science questions to be addressed in
the study of cosmic magnetic fields and will describe the observational and
theoretical opportunities and challenges afforded by the telescopes and
modelling capabilities of today and tomorrow.
