This entry will expound the main features of the notion of conscience as it is used in philosophical discussion, religious teaching and in common language alike. The perspective adopted here will be theoretical, rather than historical. The entry focuses on the Western tradition and some examples are drawn from Christian sources. The entry is structured around four possible, but not mutually exclusive, ways of conceptualizing conscience. These will be preceded by an introductory section outlining the pluralistic, morally neutral and subjective nature of the concept of conscience. The four main aspects of conscience that will be described are the following. Section 2 discusses conscience as a faculty for self-knowledge and self-assessment. Section 3 presents the epistemic aspect of conscience that allows the formation of moral beliefs, distinguishing the different possible sources of moral principles that inform such beliefs. In section 4, conscience will be described as a motivational force or as the source of our sense of duty, which already presupposes a body of moral knowledge or of moral beliefs. Finally, section 5 will focus on conscience understood as the body of personal core and self-identifying moral beliefs which is often taken to be the basis of moral integrity (Fuss 1964; Wicclair 2011) and of our sense of personal identity (Childress 1979). As discussed in section 6, this last approach to conscience is often used with a political function to advocate freedom of thought and action in liberal democratic societies, for example, as explained in subsection 6.1, through conscientious objection to practices that one would otherwise be professionally or legally expected to perform.