To which extent is it legitimate, in view of freedom of conscience and religion, to sanction individuals for refusing to take part in an activity they claim to be incompatible with their moral or religious convictions? To answer this question, this study first clarifies some of the concepts of conscientious objection. Then it examines the case law of international bodies and draws distinctions in order to differentiate several types of objections, hence identifying the evaluation criteria applicable to the respect that each one deserves. Finally, this study proposes indications as to the rights and obligations of the State in front of those different types of objections.