It is often assumed that Schumpeter made the first formulation of his evolutionary research programme in The Theory of Economic Development (Development). This assumption is misleading for at least two reasons. First, the 1934 English edition of this book is the somewhat modified translation of the second German edition of 1926 (Entwicklung II). In turn, this is the radically revised version of the first German edition of 1912 (or 1911, if we emphasise the point of time at which it became available). Second, the first edition of Theorie der wirtschaftlichen Entwicklung (Entwicklung I) is clearly a sequel to Schumpeter's first book in which he—in 1908—announced the research programme that added evolutionary economics to equilibrium economics. This book is Das Wesen und der Hauptinhalt der theoretischen Nationalökonomie (Wesen)—and it has never been translated into English. In very free translation, this book can be called ‘The Essence and Limits of Equilibrium Economics’ while the title of his second book could have been ‘The Essence of Evolutionary Economics’. Schumpeter implicitly pointed at the importance of these books by emphasising the importance of the “third decade” in the lives of great economists. This decade represents “that period of sacred fertility which, in the case of every thinker, creates what is subsequently worked out” (S1921, 87). In his own case, the results of the “period of sacred fertility” from 1903–13 were largely presented inWesen from 1908 and Entwicklung I from 1912.