What is consensus and how is it achieved in meetings? Four types of consensus decision- making [forthcoming in: The Cambridge Handbook of Meeting Science, edited by Joseph A. Allen, Nale Lehmann-Willenbrock & Steven G. Rogelberg] Christoph Haug University of Gothenburg, Dept. of Sociology and Work Science Abstract This chapter makes three central claims: first, that the term consensus has been used to identify two different phenomena, mental consensus and interactional consensus; second, that unanimity (everyone agrees) and consensus (no one disagrees) are two distinct modes of col- lective decision-making and, third, that consensus is a mode of decision-making that can be practiced in different ways, thus making it necessary to distinguish different types of consen- sus when analyzing (and practicing) consensus decision-making: imposed consensus, ac- claimed consensus, basic consensus, and deliberative consensus. These for types of consensus vary in their degree of openness towards dissenting voic- es. In an imposed consensus, it is simply claimed (e.g. by the meeting chair) that consensus has been reached with no opportunity for the meeting participants to oppose this claim. In an acclaimed consensus, in contrast, there is an explicit opportunity for participants to express their views, but its official purpose is not to express dissent but consent. In basic consensus participants are explicitly asked if there is anyone who disagrees and a stretch of audible si- lence passes before the consensual decision is confirmed. Deliberative consensus, finally, not only gives participants the opportunity to express dissent, but actively encourages that dissent is articulated in order to make sure that no one is silenced.