  Opinions are an integral part of how we perceive the world and each other.
They shape collective action, playing a role in democratic processes, the
evolution of norms, and cultural change. For decades, researchers in the social
and natural sciences have tried to describe how shifting individual
perspectives and social exchange lead to archetypal states of public opinion
like consensus and polarization. Here we review some of the many contributions
to the field, focusing both on idealized models of opinion dynamics, and
attempts at validating them with observational data and controlled sociological
experiments. By further closing the gap between models and data, these efforts
may help us understand how to face current challenges that require the
agreement of large groups of people in complex scenarios, such as economic
inequality, climate change, and the ongoing fracture of the sociopolitical
landscape.
