This chapter complements previous ones by providing microeconomic foundations for the transition from the stagnation regime to the growth regime. These microeconomic foundations consist of a simple model of individuals choosing an education investment, subject to some budget constraints. It is shown that there exists a critical threshold for the stock of knowledge below which the individual does not invest in education, and above which the investment takes place. We then examine relations between individual decisions and the long-run dynamics of knowledge accumulation and economic development.