The surviving writings of Epicurus and his followers contain several references to epibolê – a puzzling notion that does not receive discussion in the extant Epicurean texts. There is no consensus about what epibolê is, what it is of, and what it operates on and, moreover, its epistemological status is controversial. This article aims to address these issues in both Epicurus and later Epicurean authors. Part One focuses mainly on Epicurus’ Letter to Herodotus, highlights a crucial distinction hitherto unnoticed in (...) the literature between two different types of epibolê, and brings out he necessary connection between epibolê and the application of the criteria of truth. Part Two considers the philosophical merits of the traditional interpretation of epibolê as projection and/or attention. Part Three examines the two aforementioned types of epibolê in Lucretius and Philodemus and shows that these authors accord epibolê paramount epistemological and ethical importance. (shrink)