This collection of twelve original essays commissioned by Britain's Royal Economic Society commemorates the 1990 centennial of the first publication of Alfred Marshall's Principles of Economics, one of the truly seminal works in the history of the subject. Marshall, who lived from 1842 to 1924, was the founder of the Cambridge school of economics and the teacher of John Maynard Keynes. Each of the twelve essays in this volume focuses on some aspect or aspects of Marshall's work, life, or legacy. His magnum opus, the Principles, receives considerable attention, but the discussion is not narrowly restricted to that work - which was in any case only a portion of a larger project, never completed. John Whitaker's essay sets out the detailed history of Marshall's failure to complete the projected second volume of the Principles, and describes the thorny path leading to the publication of Industry and Trade in 1919 and Money Credit and Commerce in 1923.