  In this talk, I review a number of particle-physics models that lead to the
creation of magnetic fields in the early universe and address the complex
problem of evolving such primordial magnetic fields into the fields observed
today. Implications for future observations of the Cosmic Microwave Background
(CMB) are discussed. Focussing on first-order phase transitions in the early
universe, I describe how magnetic fields arise in the collision of expanding
true-vacuum bubbles both in Abelian and non-Abelian gauge theories.
