  Bell's theorem proves that quantum theory is inconsistent with local physical
models. It has propelled research in the foundations of quantum theory and
quantum information science. As a fundamental feature of quantum theory, it
impacts predictions far beyond the traditional scenario of the
Einstein-Podolsky-Rosen paradox. In the last decade, the investigation of
nonlocality has moved beyond Bell's theorem to consider more sophisticated
experiments that involve several independent sources that distribute shares of
physical systems among many parties in a network. Network scenarios, and the
nonlocal correlations that they give rise to, lead to phenomena that have no
counterpart in traditional Bell experiments, thus presenting a formidable
conceptual and practical challenge. This review discusses the main concepts,
methods, results and future challenges in the emerging topic of Bell
nonlocality in networks.
