This volume presents the lectures of the nineteenth Canary Islands Winter School, dedicated to the Cosmic Microwave Background (CMB). This relict radiation from the very early Universe provides a fundamental tool for precision cosmology. Prestigious researchers in the field present a comprehensive overview of current knowledge of the CMB, reviewing the theoretical foundations, the main observational results and the most advanced statistical techniques used in this discipline. The lectures give coverage from the basic principles to the most recent research results, reviewing state of the art observational and statistical analysis techniques. The impact of new experiments and the constraints imposed on cosmological parameters are emphasized and put into the broader context of research in cosmology. This is an important resource for both graduate students and experienced researchers, revealing the spectacular progress that has been made in the study of the CMB within the last decade.