Building a collection in academic and public libraries entails knowing the publishing market and matching it to the community to be served. This requires a guiding philosophy with goals and statements of objectives, which usually end up as part of a collection development policy. Sometimes such a policy is a formal, written document and sometimes it exists only in the minds of the people in charge of the library. In any case, one of the important aspects of collection building that never makes it into the formal policy is the evaluation of the existing collection, or, after a time, the evaluation of the one which the policy has described. In the former case it is always important to know what it is that you are building on and in the latter case it is a good indication of the success of the policy.