Resource Centre > Glossary > Opt-out and Opt-in collective actions

Opt-out collective action, once the class/group is certified, includes all those class members who have not opted out. See for instance the U.S. Class action model.

Opt-in collective action requires an act of opting in for a potential class/group member to become formally a class/group member. Most European collective litigation models (see link to our national collective litigation models section) are opt-in procedures.