2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/6075We summarize the physical mechanism by which the Cosmic Microwave Background acquires a small degree of polarization. We discuss the imprint left by gravitational waves and the use of polarization as a test of the inflationary paradigm. We discuss some physical processes that affect the CMB polarization after recombination such as gravitational lensing and the reionization of the universe.Review written for the Carnegie Observatories Centenial Symposium IIAstrophysicstext