An important issue for research librarians is the life cycle cost of acquiring and maintaining a collection. While purchase costs are easy to identify, associated acquisition, cataloging, circulation, and maintenance expenses are difficult to measure and attribute to specific collections. This paper develops a methodology to determine the life cycle costs of collections based on readily available statistical data collected annually by the Association of Research Libraries (ARL). ARL cost data (e.g., salaries and wages, materials expenditures, and operating expenses) for a specific library are allocated to collections (e.g., manuscripts, serials, and microforms) based on the size of the collection and its relative space requirements. By aggregating allocated costs, total life cycle costs for a collection can be estimated. Results of this research indicate that life cycle costs of collections are many multiples of their purchase costs. Results further suggest that the life cycle costs of monograph collections overwhelm the costs of other collections in research libraries - the cost structure of a research library is largely driven by its monograph collection. These results should prove useful in efforts to control costs and improve performance in research libraries.