Librarians are well known as gatherers of statistics and other data. However, we do not always use the information that we gather, preferring instead to point to the numbers themselves as evidence of our work. This presentation attempted both to describe the benefits and drawbacks of numerous ways to accumulate information about our collections and library services and to show how that information can be used to make collection management decisions. The types of data to be described include usage statistics, subject–date analysis, bibliography or peer comparisons, patron input, cost-per-use, wear and tear, and anecdotal evidence. No one method of gathering data will give a complete picture. However, using a combination of data gathering methods can help to give an overall picture of the strengths and weaknesses of a given collection and give clues about what areas may need development—or can be ignored.