  The magnetic field of the Sun is the underlying cause of the many diverse
phenomena combined under the heading of solar activity. Here we describe the
magnetic field as it threads its way from the bottom of the convection zone,
where it is built up by the solar dynamo, to the solar surface, where it
manifests itself in the form of sunspots and faculae, and beyond into the outer
solar atmosphere and, finally, into the heliosphere. On the way it, transports
energy from the surface and the subsurface layers into the solar corona, where
it heats the gas and accelerates the solar wind.
