Over 10% of US employees now regularly work from home (WFH), but there is widespread skepticism over its impact and worries about “shirking from home”. We report the results of a WFH experiment at CTrip, a 16,000 employee NASDAQ-listed Chinese multinational. Call center employees who volunteered to WFH were randomly assigned to work from home or in the office for 9 months. Working from home led to a 13% performance increase, of which about 8.6% is from working more minutes per shift (fewer breaks and sick-days) and 4% from more calls per minute (attributed to a quieter working environment). Home workers also reported improved work satisfaction and their job attrition rate fell by 50%. After the experiment, the firm rolled the program out to all employees, letting them choose home or office working. Interestingly, only half of the treatment group decided to work at home, with the other half reallocating in favor of office working. After employees were allowed to choose where to work, the performance impact of WFH almost doubled, highlighting the benefits of choice when adopting modern management practices like home working.