Beneath the floor, between the shelves, propping up the website: you may not be able to see the data in a modern library, but it underpins every book, e-resource and service. Whether user activity data, subscription data or financial information, this vital business intelligence allows librarians to make decisions like: which books should we buy on next year’s budget? When are the journal subscriptions due, and which to renew? How popular are our online portals with staff and students? And, inevitably, where can we make savings? Of course, to curate this kind of information means maintaining data accurately, and that has become a crucial skill – and expense – for library managers.