Teachers often characterize their interest in and commitment to the profession as moral: a desire to support students, serve their communities, or uphold civic ideals embedded in the promise of public education. These initial and sustaining moral impulses are well documented in research on teaching and teacher education. However, moral commitments can also be a source of teachers’ dissatisfaction and resistance, especially in the age of the market-based Global Education Reform Movement. This article explores the phenomenon of conscientious objection in teaching as an enactment of professional ethics. Conscientious objection describes teachers’ actions when they take a stand against job expectations that contradict or compromise their professional ethics. Teachers who refuse to enact policies and practices may be represented by popular media, school leaders, policymakers, and educational researchers as merely recalcitrant or insubordinate. This perspective misses the moral dimensions of resistance. Teachers may refuse to engage in practices or follow mandates from the standpoint of professional conscience. This article also highlights varieties of conscientious objection that are drawn from global examples of teacher resistance. Finally, the article explores the role of teachers unions as potential catalysts for collective forms of conscientious objection.