Bernard Lonergan's Insight: A Study of Human Understanding is one of the most profound and challenging books of the 20th century. In it he tries to answer the philosophical questions raised by Kant, with the resources provided by Thomas Aquinas, updated with questions of the 20th century. This book is a comprehensive explanation, commentary and criticism of Lonergan's work, which no one, according to the author, has previously attempted. As such it would be of assistance to anyone trying to penetrate Lonergan's profound but difficult work.