This book publishes for the first time the manuscript notes Robbins used for his lectures on the Principles of Economic Analysis from 1929/30 to 1934/40. At the outset of his career he took the advice of a senior colleague to prepare his lectures by writing them out fully before he presented them. He intended to turn his lecture notes into a book, abandoning the project only when he was asked to chair the Committee on Higher Education in 1960. This volume is not exactly the book he wanted to write, but it is a unique record of what was taught to senior undergraduate and graduate economists in those 'years of high theory'.