While State and lower Federal courts have approved package or containment plea agreements granting one defendant more lenient treatment if a second defendant pleads guilty, the Supreme Court has not yet addressed the propriety of such agreements. The article examines the constitutional challenges to package plea bargaining, including the possibility of coercion when multiple defendants are related to one another. In proposing contingent plea offers to related and unrelated co-defendants, prosecutors must exercise good faith, for there are dangers that one defendant may pressure another to plead guilty. Judges presiding over package plea bargaining have an obligation to define appropriate standard practice among prosecutors purporting to offer containment plea bargains, and they should conduct hearings to examine the attorneys' reasons for offering package plea bargains. For their part, prosecutors should take a restrictive approach to proposing package plea offers and should use them only to conserve prosecutorial resources when the trial of the jointly-charged multiple defendants would not be much longer than the trial of any single defendant. (Author abstract modified.) 146 footnotes.