Monetary policy is typically made by a committee. Economists frequently view this as desirable: Two heads are better than one. This chapter reviews the literature challenging this view. It focuses on process losses, specifically the failure of groups to share information effectively and the tendency of members to free ride in the costly acquisition of information. It discusses what the literature suggests might mitigate these problems. It reviews the literature detailing how groups change their members, tending to polarize them and increase their overconfidence, so that committee decisions are more extreme than the predeliberation mean view of their members, and members are more certain their choices are correct. It describes extreme pathologies that might afflict monetary policy committees: groupthink, the Abilene paradox, and polythink. It discusses the features of monetary policy committees that might reduce the likelihood of these pathologies occurring. Two features of monetary policy committees that might be important determinants of their performance are their size and composition. This chapter reviews the literature on the optimal size and diversity of monetary policy and other committees.