None of the works included among Erasmus’ ‘Literary and Educational Writings’ in the Collected Works of Erasmus captures his most adventurous thinking about how texts signify in – and thereby make or remake – worlds of thought, feeling, and action. The one that comes closest to doing so, the Ratio verae theologiae (‘A System of True Theology’), was first published separately in 1518 and 1519, then appeared in the preliminaries to the New Testament in Erasmus’ (revised) 1519 edition.This handy Ratio or compendious ‘System’ gave advice on how to interpret complex texts and develop persuasive arguments based upon them. Its lessons were applied to the canonical Scriptures as source, and to everyday Christian theology as target discourse. They unfold in response to the special difficulties and incitements of the biblical text in Latin and Greek, within a framework provided by classical grammar and rhetoric, adjusted to the examples of the Church Fathers as exemplary interpreters of the Bible. At every turn, the Ratio reveals the instincts and intuitions of an exceptional theorist and practitioner of the cognitive, social, and political arts of written language. This student edition, the first of its kind in any language, is based on the translation and notes by Robert D. Sider in the Collected Works of Erasmus Volume 41. It is designed to make it easier to estimate the long-term value of this particular work and of Erasmus’ works more generally, and to allow for a multidisciplinary understanding of the lives of human beings as symbol-using creatures in worlds constructed partly by texts.