  A compact overview of the status of CMB anisotropy results and their
cosmological interpretation. Section headings: Introduction; CMB Spectrum;
Description of CMB Anisotropies; Cosmological Parameters; Physics of
Anisotropies; Current Anisotropy Data; CMB Polarization; Complications;
Constraints on Cosmological Parameters; Particle Physics Constraints;
Fundamental Lessons; and Future Directions. This 2023 replacement is a
substantial update compared with earlier versions of this review posted to the
arXiv.
