This chapter first offers an overview of key concepts in The Sickness unto Death, such as human nature, self, despair, and wholeheartedness. It then discusses the relation between Part One and Part Two of The Sickness unto Death, offering a comparison of different types of despair (or doublemindedness). In this connection, it discusses the relations between faith and reason, and philosophy and theology. It is argued that the relatively neglected Part Two of The Sickness unto Death, entitled “Despair is Sin,” reinterprets the problem of despair from Part One by introducing the Christian concept of sin. In Part Two, sin represents an unwillingness to be oneself before God that involves self-deception. Overcoming despair, on the other hand, requires an unconditional will to be oneself before God. However, the latter does not accept everything as it is but rather hopes against hope to reconcile ideals with reality. For Kierkegaard, this hope is interconnected with Christian faith, charity, and moral commitment. Indeed, overcoming despair by forming a wholehearted or coherent self represents a fundamental moral and religious task according to Kierkegaard.