This volume contains the lectures and talks given at the International School of Physics “Enrico Fermi” entitled New Horizons for Observational Cosmology, which was held in the town of Varenna, by the lake Como, from July 1 to July 6, 2013.

This School came at a very unique and exciting time in cosmology. Our understanding of the universe has been revolutionized by observations of the cosmic microwave background, the large-scale structure of the universe, and distant supernovae. These studies have conclusively shown that we are living in a strange universe: 96% of the present-day energy density of the universe is dominated by the so-called dark matter and dark energy. However, we do not know what dark matter and dark energy actually are. The data also suggest that it is likely that the universe underwent a rapid accelerating expansion phase in the very early universe called the inflationary phase. However, we still do not know how inflation happened. Now, we are about to have another revolution in cosmology because, during the next couple of years, we expect to see a further qualitative jump in our knowledge of the universe. The Planck satellite collaboration, mostly funded by ESA, in particular, just published the cosmological results from its first year of survey. These results, while confirming again in a spectacular way the expectations of the standard cosmological scenario, are also hinting to the presence of some tensions or deviations from the standard scenario that need further investigations.

The future Planck data release expected around the end of 2014 will provide an essentially complete view of temperature anisotropy of the cosmic microwave background, as well as full-sky maps of polarised emission at many frequencies. These data may resolve some of the current tensions, and also provide important information on the polarised Galactic foregrounds. A host of ground-based experiments measuring polarisation of the cosmic microwave background (e.g., ACTpol, SPTpol, Polarbear, BICEP2/Keck Array) are also in the process of reporting their results soon. The next-generation galaxy surveys (BOSS, DES, HSC, HETDEX) will begin to yield data. These new data will undoubtedly address fundamental questions about the universe: what is the nature of dark energy and dark matter? What powered the Big Bang? Did inflation occur? If it did, how did it occur? What is the mass of neutrinos? When and how were the first stars and galaxies formed?

Maybe some answers to these exciting questions will come from the future work of the excellent students that attended our School.

A. Cooray, E. Komatsu, A. Melchiorri and L. Lamagna