A co-operative federation or secondary co-operative is a co-operative in which all members are, in turn, co-operatives. Historically, these have predominantly come in the form of co-operative wholesale societies, and co-operative unions. Co-operative federations are a means through which co-operatives can fulfill the sixth Rochdale Principle, co-operation among co-operatives, with the ICA noting that “Co-operatives serve their members most effectively and strengthen the co-operative movement by working together through local, national, regional and international structures.”