In conjunction with a multi-year renovation of Concordia University's main library, a comprehensive collections reconfiguration project was launched. The new library floor plans provided for increased study space and a reduced footprint for stacks. Significant deselection of physical format materials such as circulating books, reference works, government publications, and microforms was therefore necessary in order to achieve the necessary space reduction and still maintain room for growth. Although different weeding strategies were developed for specific collections and disciplines, the key factors considered were usage, currency and duplication. By focusing on reducing duplication - multiple copies, superseded editions, replication across different formats - and using data extracted from the library system, it has been possible to remove a large volume of items with minimal decision making required from subject librarians. Virtually all weeded materials have been sent to a non-profit reseller or recycled, in keeping with the university's commitment to environmental sustainability. This approach has resulted in the removal of over 60,000 duplicate copies from the monograph collection alone. At the same time access has been retained to most unique content within the collection, allaying faculty concerns about library deselection. In less than two years the original goals of space reduction for print and microform holdings have been exceeded.