In social choice theory, the majority rule (MR) is a social choice rule which says that, when comparing two options (such as bills or candidates), the option preferred by more than half of the voters (a majority) should win.

In political philosophy, the majority rule is one of two major competing notions of democracy. The most common alternative is given by the utilitarian rule (or other welfarist rules), which identify the spirit of liberal democracy with the equal consideration of interests. Although the two rules can disagree in theory, political philosophers beginning with James Mill have argued the two can be reconciled in practice, with majority rule being a valid approximation to the utilitarian rule whenever voters share similarly-strong preferences. This position has found strong support in many social choice models, where the socially-optimal winner and the majority-preferred winner often overlap.

Majority rule is the most common social choice rule worldwide, being heavily used in deliberative assemblies for dichotomous decisions, e.g. whether or not to pass a bill. Mandatory referendums where the question is yes or no are also generally decided by majority rule. It is one of the basic rules of parliamentary procedure, as described in handbooks like Robert's Rules of Order.

In elections with more than two candidates, majority-rule is generalized by Condorcet's majority-rule principle, which states that if most voters prefer option A to option B (rank A over B), then A should defeat B unless there is a Condorcet paradox.

A common alternative to the majority rule is the plurality-rule family of voting rules, which includes ranked choice voting (RCV), two-round plurality, and first-preference plurality. These rules are often used in elections with more than two candidates. Such rules elect the candidate with the most votes after applying some voting procedure, even if a majority of voters would prefer some other alternative.

Systems in the plurality-rule family share several major features like center squeeze and tend to produce similar results. Plurality rule is often contrasted with the two other major families of voting rules, the evaluative rules and the majority (or Condorcet) rules.

The utilitarian rule, and cardinal social choice rules in general, take into account not just the number of voters who support each choice but also the intensity of their preferences.

Philosophers critical of majority rule have often argued that majority rule does not take into account the intensity of preference for different voters, and as a result "two voters who are casually interested in doing something" can defeat one voter who has "dire opposition" to the proposal of the two, leading to poor deliberative practice or even to "an aggressive culture and conflict"; however, the median voter theorem guarantees that majority-rule will tend to elect "compromise" or "consensus" candidates in many situations, unlike plurality-rules (see center squeeze).