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n. the procedure under which a third party may join an on-going lawsuit, providing the facts and the law issues apply to the intervenor as much as to one of the existing contestants. The determination to allow intervention is made by a judge after a petition to intervene and a hearing on the issue. Intervention must take place fairly early in the lawsuit, shortly after a complaint and answer have been filed and not just before trial since that could prejudice one or both parties who have prepared for trial on the basis of the original litigants. Intervention is not to be confused with joinder, which involves requiring all parties who have similar claims to join in the same lawsuit to prevent needless repetitious trials based on the same facts and legal questions, called multiplicity of actions.