My dissertation project consists of a series of historical case studies analyzing the construction, manipulation, and circulation of the neoclassical growth model. Published in 1956, this model would become one of the paradigmatic theoretical models of modern macroeconomics. Building on archival material, published work, and unpublished manuscripts, each of my case studies focuses on the specific mathematical, and statistical objects that were used to create knowledge about economic growth: the newly created national income accounting framework that was applied to search for the “sources” of growth; planning techniques from wartime research that went into constructing linear equation systems for the “rational organization” of production; and topological existence proofs, which helped formulating the concept of a “balanced growth path.” Before the background of these different mathematical, quantitative, and model versions of a growing economy, Solow’s “simple model of economic growth” developed as a rather incidental by-product. Initially thought of as a “design” for more complex empirical models, it soon became accepted as a particularly simple, clear-cut, and easy-to-use standard. Labeled “the neoclassical growth model,” it circulated widely: it was used as a prototype for large-scale planning models, it became famous for providing an instrument for measuring “technical progress,” and it is presented as a device for teaching mathematical modeling until the present day.