Book IV of Lucretius’ great philosophical poem deals mainly with the psychology of sensation ad thought. The heart of this book is a new text, incorporating the latest scholarship on the text of Lucretius, with a clear prose facing translation. The commentary concentrates on the thought of the text (relating it to other philosophers beside Epicurus) and the poetry of the Latin, placing the text in relation to Roman literature in general, and attempting to demonstrate the poetic genius of Lucretius. The introduction deals with the didactic tradition in ancient literature and Lucretius’ place in it, the structure of De Rerum Natura, the salient features of the philosophy of Epicurus and the transmission of the text.