Must good deeds be rewarded and wrongdoers punished? Would God be unjust if he failed to punish and reward? And what is it about good or evil actions and moral identity that might generate such necessities? These were some of the vital religious and philosophical questions that eighth and ninth-century Mu'tazilite theologians and their sophisticated successors attempted to answer, giving rise to a distinctive ethical position and one of the most prominent and controversial intellectual trends in medieval Islam.The Mu'tazilites developed a view of ethics whose distinguishing features were its austere moral objectivism and the crucial role it assigned to reason in the knowledge of moral truths. Central to this ethical vision was the notion of moral desert, and of the good and evil consequences - reward or punishment - deserved through a person's acts. "Moral Agents and Their Deserts" is the first book-length study of this central theme in Mu'tazilite ethics, and an attempt to grapple with the philosophical questions it raises. At the same time, it is a bid to question the ways in which modern readers, coming to medieval Islamic thought with a philosophical interest, seek to read and converse with Mu'tazilite theology. "Moral Agents and Their Deserts" tracks the challenges and rewards involved in the pursuit of the right conversation at the seams between modern and medieval concerns.