Open membership to all persons implies that there should not be a high threshold to become a member. Generally a member's share in a consumer co-operative is set at a nominal rate, although members may also be encouraged to make a contribution to the co-operative's capital. Membership shares which provide equity capital tend to be much higher to finance business operations in producer or worker co-operatives. However, if the share capital required to become a member is set at a high level, it may be a barrier to people joining a co-operative. Where significant share capital is necessarily required from new members, arrangements for payment over time, such as instalment payments, or credit facilities from an associated co-operative bank or credit union, should be made available.

Membership of secondary co-operatives, which are co-operatives that provide services to other co-operatives, should also be open without arbitrary restriction to any co-operative able to use the services the secondary co-operative provides. In some jurisdictions membership of secondary organisations is mandatory. Like primary co-operatives, membership share capital required to become a member should not be set in a way that restricts membership or is unaffordable to new or smaller co-operatives.