Knut Wicksell was an important thinker of the second-generation marginalist school, and here is his detailed commentary on and elaboration of the capital theory of Eugen von Böhm-Bawerk. It was first published in 1893, but did not appear in English until 1954. But its appearance filled a gap in the history of economic ideas. He further defends the relationship between the natural rate of interest and the return on capital. He sides strongly with the Mengerian school of marginalists against the Jevons and Walrasian branch. This book is essential for any student of Austrian capital theory. His rigor and attention to detail is impressive by any standard. This softcover book is 184 pages with index, and a foreword by G.L.S. Shackle (who mistakenly suggests that Wicksell was a proto-Keynesian).