http://www.lawlib.state.ma.us/source/mass/rul...

Massachusetts Civil Procedure Rule 23: Class Actions
[Disclaimer]

(a) Prerequisites to Class Action. One or more members of a class may sue or be sued as representative parties on behalf of all only if (1) the class is so numerous that joinder of all members is impracticable,(2) there are questions of law or fact common to the class,(3) the claims or defenses of the representative parties are typical of the claims or defenses of the class, and (4) the representative parties will fairly and adequately protect the interests of the class.

(b) Class Actions Maintainable. An action may be maintained as a class action if the prerequisites of subdivision (a) are satisfied, and the court finds that the questions of law or fact common to the members of the class predominate over any questions affecting only individual members, and that a class action is superior to other available methods for the fair and efficient adjudication of the controversy.

(c) Dismissal or Compromise. A class action shall not be dismissed or compromised without the approval of the court. The court may require notice of such proposed dismissal or compromise to be given in such manner as the court directs.