I explore the increasingly important issue of cooperation in immoral actions, particularly in connection with healthcare. Conscientious objection, especially as pertains to religious freedom in healthcare, has become a pressing issue in the light of the US Supreme Court judgement in Hobby Lobby. Section ‘Moral evaluation using the basic principles of cooperation’ outlines a theory of cooperation inspired by Catholic moral theologians such as those cited by the court. The theory has independent plausibility and is at least worthy of serious consideration—in part because it is an instance of double-effect reasoning, which is also independently plausible despite its association with moral theology. Section ‘Case study: Burwell v. Hobby Lobby’ examines Hobby Lobby in detail. Even if the judgement was correct in that case the reasoning was not, as it involved applying a ‘mere sincerity’ test to the cooperation question. The mere sincerity test leads to absurd consequences, whereas a reasonableness test applied using the theory of cooperation defended here would avoid absurdity. Section ‘A question of remoteness: “accommodations” and opt-outs’ explores the post-Hobby Lobby problem further, examining opt-outs and accommodations: the Little Sisters of the Poor case shows how opt-outs are misunderstood on a mere sincerity test, which the court rightly rejected. Section 'Application to the medical field: Doogan and Wood’ discusses the UK case of Doogan and Wood, concerning participation in abortion. Again, a judicially recognised ethic of cooperation, if it were part of the fabric of legal reasoning in such cases, would have enabled the conscientious objectors in this and similar situations to have their freedom of conscience and religion respected in a way that it currently is not.