This book presents, for the first time, a detailed transcription of Jacob Viner's Ecomics 301 class as taught in 1930. These lecture tes provide insight into the legacy of Jacob Viner, whose seminal contributions to fields such as international ecomics and the history of ecomics are well kwn, but whose impact in sparking the revival of Marshallian microecomics in the United States via his classroom teaching has been less appreciated. Generations of graduate students at the University of Chicago have taken Ecomics 301. The course has been taught by such luminaries as Milton Friedman and Gary Becker, and remains an introduction to the analytical tools of microecomics and the distinctive Chicago way of thinking about the market system. This demanding and rigorous course first became famous in the 1930s when it was taught by Jacob Viner. When read in tandem with the Transaction editions of Milton Friedman's Price Theory, Frank Knight's The Ecomic Organization, and Gary Becker's Ecomic Theory, Viner's lectures provide the reader with important insights into the formative period of Chicago price theory. These recently discovered tes from Viner's class will be important for historians of ecomic thought and anyone interested in the origins of the Chicago School of Ecomics.