The many sources of generation of magnetic field are derived from a generalized Ohm's law. These sources include the [Formula: see text] effect, anisotropic pressure, as well as the effect of the quiver velocity associated with the incident laser beam. The magnetic field can be generated either through some imposed lack of spherical symmetry or through an instability. Among the latter, the collisional Weibel instability appears to be the most important. Convection and amplification can occur through the Nernst effect, and the resulting magnetic-field structure can inhibit fast-electron transport. Dynamo action and diffusion processes are also included in this review.