Nicolas Malebranche is now recognised as a major figure in the history of philosophy, occupying a crucial place in the Rationalist tradition of Descartes, Spinoza and Leibniz. The Search after Truth is his first, longest and most important work; this volume also presents the Elucidations which accompanied its third edition, the result of comments that Malebranche solicited on the original work and an important repository of his theories of ideas and causation. Together, the two texts constitute the complete expression of his mature thought, and are written in his subtle, argumentative and thoroughly readable style. They are presented in the distinguished translations by Thomas M. Lennon and Paul J. Olscamp, together with a historical introduction, a chronology of Malebranche's life, and useful notes on further reading.