  The origin of population-scale coordination has puzzled philosophers and
scientists for centuries. Recently, game theory, evolutionary approaches and
complex systems science have provided quantitative insights on the mechanisms
of social consensus. However, the literature is vast and widely scattered
across fields, making it hard for the single researcher to navigate it. This
short review aims to provide a compact overview of the main dimensions over
which the debate has unfolded and to discuss some representative examples. It
focuses on those situations in which consensus emerges 'spontaneously' in
absence of centralised institutions and covers topic that include the
macroscopic consequences of the different microscopic rules of behavioural
contagion, the role of social networks, and the mechanisms that prevent the
formation of a consensus or alter it after it has emerged. Special attention is
devoted to the recent wave of experiments on the emergence of consensus in
social systems.
