The concept of merit plays an important role in the medieval discussion of justification. Although it was widely considered to be unacceptable to allow that human beings could be said to earn or deserve their justification, in the strict sense of the terms, the concept of merit was developed extensively to allow a strict concept of merit (usually referred to as ‘condign merit’) to be distinguished from a weaker sense of merit (usually referred to as ‘congruous merit’). The chapter opens by considering how Augustine’s concept of merit was complexified during the Middle Ages, and the reason for this process. Particularly within Franciscan schools of theology, there was a widespread recognition of a gradation of forms of merit, including the notion of merit as a self-imposed divine obligation. This chapter explores these divergences, and notes the growing tendency on the part of writers such as Duns Scotus and William of Ockham to adopt voluntarist rather that intellectualist approaches to merit, locating the ground of merit in God’s decision to accept certain actions as meritorious. The chapter concludes by noting the continuity between these later medieval lines of thought and those associated with the Reformation – such as John Calvin’s understanding of the grounds of the merit of Christ, on which human salvation was held to be contingent.