Isaac Newton wrote the manuscript Questiones quaedam philosophicae at the very beginning of his scientific career. This small notebook thus affords rare insight into the beginnings of Newton's thought and the foundations of his subsequent intellectual development. The Questiones contains a series of entries in Newton's hand that range over many topics in science, philosophy, psychology, theology, and the foundations of mathematics. These notes, written in English, provide a very detailed picture of Newton's early interests, and record his critical appraisal of contemporary issues in natural philosophy. Written predominantly in 1664–5, they give a significant perspective on Newton's thought just prior to his annus mirabilis, 1666. This volume provides a complete transcription of the Questiones, together with an 'expansion' into modern English, and a full editorial commentary on the content and significance of the notebook in the development of Newton's thought. It will be essential reading for all those interested in Newton and the intellectual foundations of science.