This book is devoted to a systematic discussion of the physics of the cosmic microwave background. This field of physics is very complex and involves an enormous diversity of processes that occur in the course of expansion of the Universe. The CMB proved to be a true ‘goldmine’ for extracting scientific information on these processes; it has in fact grown into the central branch of modern cosmology. Comparing this highly perfected theory with observational data makes it possible to obtain essential information on the early Universe and on the physical parameters of the Universe as a whole.

Combining these results with results from other branches of astrophysics, such as the large-scale structure of the Universe, supernovae, etc., provides a robust basis of modern cosmology.

Results from BOOMERANG, MAXIMA-1, ARCHEOPS, CBI, DASI and WMAP were so important that they have taken the field into the era of ‘precision cosmology’. As we have discussed, these studies have produced impressive constraints on many fundamental cosmic parameters and have led to a very definite picture of the structure and evolution of the Universe. As a result, one could become overexcited and declare that almost everything in cosmology is now known. However, we want to emphasize that even after those remarkable projects, the study of CMB physics is not coming to an end. There are still many unsolved problems in cosmology, and another generation of satellite experiments, as well as ground-based and balloon-borne experiments, is needed.