Abstract In the Renaissance, Epicureanism and other heterodox scientific theories were strongly associated with heresy and atheism, and frequently condemned. Yet, when Lucretius's Epicurean poem De Rerum Natura reappeared in 1417, these associations did not prevent the poem's broad circulation. A survey of marginalia in Lucretius manuscripts reveals a characteristic humanist reading agenda, focused on philology and moral philosophy, which facilitated the circulation of such heterodox texts among an audience ...