Anna has a part-time job at the grocery shop, a short bike ride from the School of Economics. The job gives her an income she can spend on things she enjoys, but it also takes up time. “How many hours a week should I work?” she asks herself. We analyse labour supply as a trade-off between the joy of leisure and the joy of consumption. More leisure means fewer hours at work—and therefore less money to spend. The optimal choice is determined by prices (in this case, the real wage, meaning the wage divided by the price of goods) and by preferences, just as in the previous two chapters. Consumer theory can also be used to study career choice. A managerial position has opened up at the grocery shop—a job that would give Anna greater responsibilities but much less free time. What wage would make her willing to take on that role? Sometimes we receive money without working for it—for instance, a gift from a generous grandfather or unemployment benefits from the government. Toward the end of the chapter, we examine how such non-labour income influences labour supply.