This chapter examines the arguments set forth to explain why the Jews became a population of skilled craftsmen, traders, bankers, and physicians and why they created a worldwide urban diaspora. These arguments are grouped into two main categories: ones that highlight exogenous factors (discrimination, restrictions, persecutions, massacres) and ones that emphasize endogenous choices (voluntary self-segregation in order to maintain religious rites, voluntary migration to cities to preserve group identity). The chapter then presents the thesis that in a world populated by illiterate people, the ability to read and write contracts, business letters, and account books using a common alphabet gave the Jews a comparative advantage over other people. The Jews also developed a uniform code of law (the Talmud) and a set of institutions (rabbinic courts, the responsa) that fostered contract enforcement, networking, and arbitrage across distant locations. Thus, high levels of literacy and the existence of contract-enforcement institutions became the levers of the Jewish people.