In a field study conducted at a leading Fortune 100 company, we examined how having development teams reside in their own large room (an arrangement called radical collocation) affected system development. The collocated projects had significantly higher productivity and shorter schedules than both the industry benchmarks and the performance of past similar projects within the firm. The teams reported high satisfaction about their process, and both customers and project sponsors were similarly highly satisfied. The analysis of questionnaire, interview and observational data from these teams showed that being "at hand," i.e. both visible and available, helped them to coordinate their work better and learn from each other. Radical collocation seems to be one of the factors leading to high productivity in these teams.