Doing and Being confronts the problem of how to understand two central concepts of Aristotle’s philosophy: energeia and dunamis. While these terms seem ambiguous between actuality/potentiality and activity/capacity, Aristotle did not intend them to be so. Through a careful and detailed reading of Metaphysics Theta, Beere argues that we can solve the problem by rejecting both actuality and activity as translations of energeia, and by working out an analogical conception of energeia. This approach enables Beere to discern a hitherto unnoticed connection between Plato’s Sophist and Aristotle’s Metaphysics Theta, and to give satisfying interpretations of the major claims that Aristotle makes in Metaphysics Theta, the claim that energeia is prior in being to capacity (Theta 8) and the claim that any eternal principle must be perfectly good (Theta 9).