The action within the Sun whereby the kinetic energy of the hot, highly ionized gas of the solar interior is converted into the magnetic field that gives rise to solar activity. In the standard picture due to H. W. Babcock, magnetic field lines running from pole to pole within the Sun (the poloidal field) are twisted parallel to the equator (the toroidal field) by the Sun’s differential rotation. The distorted magnetic field rises up through the photosphere to form active regions, including sunspots. Convection currents gradually turn the toroidal field into a poloidal field of the reverse direction for the next cycle.