How does remote work affect productivity and how productive are workers who choose remote jobs? We estimate both effects in a U.S. Fortune 500 firm’s call centers that employed both remote and on-site workers in the same jobs. Prior to COVID-19, remote workers answered 12 percent fewer calls per hour than on-site workers. When the call centers closed due to COVID-19, the productivity of formerly on-site workers declined by 4 percent relative to already-remote workers, indicating that a third of the initial gap was due to a negative treatment effect of remote work. Yet an 8 percent productivity gap persisted, indicating that the majority of the productivity gap was due to negative worker selection into remote work.