Amidst the rise of remote work, how does proximity to colleagues affect workers? We find working near colleagues leads to a tradeoff, increasing long-run human capital development at the expense of short-term output. We study software engineers at a Fortune 500 firm, whose main campus has two buildings several blocks apart. When offices were open, engineers working in the same building as all their teammates received 22 percent more online feedback than engineers with distant teammates. After offices closed for COVID-19, this advantage largely disappears. Yet sitting together reduces engineers’ programming output, particularly for senior engineers. The tradeoffs from proximity are more acute for women, who both do more mentoring and receive more mentorship when near their coworkers. Proximity impacts career trajectories, dampening short-run pay raises but boosting long-run outcomes. These results can explain national trends: those who need mentorship and those who can provide it are more likely to work from the office. However, even if most mentors and mentees go into the office, remote work may reduce interaction: pre-COVID, having just one distant teammate reduced feedback among co-located workers.