According to its constitutions ("Charters"), Rotary defines itself as a non-partisan, non-sectarian organization. It is open to business and professional leaders of all ages and economic status. Its membership tends towards the middle-aged and wealthy.

Active membership is by invitation from a current Rotarian, to professionals working in diverse areas of endeavor. Each club can have up to ten per cent of its membership representing each business or profession in the area it serves. The goal of the clubs is to promote service to the community they work in, as well as to the wider world. Many projects are organized for the local community by a single club, but some are organized globally.

Honorary membership is given by election of a Rotary Club to people who have distinguished themselves by meritorious service in the furtherance of Rotary ideals. Honorary membership is conferred only in exceptional cases. Honorary members are exempt from the payment of admission fees and dues. They have no voting privileges and are not eligible to hold any office in their club. Honorary membership is time limited and terminates automatically at the end of the term, usually one year. It may be extended for an additional period or may also be revoked at any time.

From 1905 until the 1980s, women were not allowed membership in Rotary clubs, although Rotarian spouses, including Paul Harris's wife, were often members of the similar "Inner Wheel" club. Women did play some roles and Paul Harris' wife made numerous speeches. In 1963, it was noted that the Rotary practice of involving wives in club activities had helped to break down female seclusion in some countries. Clubs such as Rotary had long been predated by women's voluntary organizations, which started in the United States as early as 1790.

Interestingly, the Irish clubs had discussed admitting women in 1912 but the proposal floundered over class issues.

Gender equity in Rotary International was first publicly raised by the Duarte Rotary Club affair. In 1976, the Duarte California club allowed three women to join. Rotary International expressed alarm but requests to terminate the women's memberships were rejected by the club. As a result, Rotary International revoked the club's charter in 1978. The Duarte club filed suit in the California courts, claiming that Rotary Clubs are business establishments subject to regulation under California's Unruh Civil Rights Act, which bans discrimination based on race, gender, religion or ethnic origin. Rotary International then appealed the decision to the U.S. Supreme Court. The RI attorney argued that "... [the decision] threatens to force us to take in everyone, like a motel". The Duarte Club was not alone in opposing RI leadership; the Seattle-International District club unanimously voted to admit women in 1986. The United States Supreme Court, on May 4, 1987, confirmed the Californian decision and, since that time, women have been allowed to join Rotary. The Elks, the final holdout among service clubs in prohibiting female membership, voted in 1995 to allow women. By 2007, there was a female director of Rotary International while female district governors and club presidents were common. Women accounted for 15% of International membership (22% in North America). The change of the second Rotarian motto in 2004, from "He profits most who serves best" to "They profit most who serve best", 99 years after its foundation, illustrates the move to general acceptance of women members in Rotary.