This dissertation argues that conduct and behavior were believed essential for determining one's post-mortem fate from the earliest periods of both ancient Egypt and ancient Greece. Part one of this four-part study examines Plato's eschatological myths and provides a complete catalog and brief discussion of all references in them to conduct and behavior that affect one's fate in the afterlife. Part two traces the evolution of the concept of the afterlife from Homer to the Dramatists, also cataloging all references to the afterlife that mention conduct and behavior. This part of the study demonstrates that the concept of reward and retribution in an afterlife, based on conduct in this life, is already found in Homer. However, it is in Pythagorean and Orphics circles of Greater Greece that it reaches its most dramatic development and from that milieu provides such an enormous impact on Plato. The third part deals with the connection between conduct and the afterlife in ancient Egypt up to the time of the Book of the Dead. An extensive catalog of Egyptian virtues and vices that have afterlife consequences is compiled from the religious texts of the 5th to 18th Dynasty. In part four, the relationship between conduct and behavior and the afterlife beliefs of the two societies are compared and contrasted. In the earliest periods, the afterlife texts appear to be concerned only with the elite: the king in Egyptian 5th Dynasty Pyramid Texts and the heroes in Homeric and Hesiodic Greece. This study argues that there is some evidence in the early texts of both societies for a belief that commoners could also be rewarded or punished in an afterlife. In later periods both societies' religious texts dealing with the afterlife exhibit a much more developed democratization. As post-mortem beliefs became more democratic, conduct and behavior grew in importance. However, from the earliest time periods, both societies believe that the gods, primarily Maat in Egypt and Dike in Greece, are responsible for the proper ordering of the cosmos and that violations of that order will call down the most dire consequence -- the loss of a beneficent afterlife.