Pre-industrial apprenticeship is often considered more stable than its nineteenth- and twentieth-century counterparts, apparently because of the more durable relationships between masters and apprentices. Nevertheless, recent studies have suggested that many of those who started apprenticeships did not finish them. New evidence about more than 7,000 contracts across several cities in three countries finds that, for a number of reasons, a substantial minority of youths entering apprenticeship contracts failed to complete them. By allowing premature exits, cities and guilds sustained labor markets by lowering the risks of entering long training contracts. Training flexibility was a pragmatic response to labor-market tensions.