More choice in formats for library customers may mean more constraints on choices in materials acquisition. An increase in the number of formats libraries provide may, over time, substantially alter the quality and diversity of library collections. This ERIC Digest examines some of the costs and challenges presented by format proliferation and some strategies for addressing those challenges, particularly when an increase in the total budget for acquisitions is not a possibility. Discussion includes the role of audiovisual (AV) materials in increasing circulation and library visits, and the need for more study of current lending patterns to establish a clear mandate for unashamed purchase of AV materials by traditionally print-oriented librarians; the effect of format proliferation in radically changing the depth and diversity of a collection; and what public libraries can do to meet the challenges of offering format choice while maintaining quality of the collection. To avoid sacrificing quality and depth, libraries must be acutely aware of customer needs, be sure that the library has a clear and fiscally realistic focus of purpose, and cooperate with other libraries to share resources. (AEF)