The Association of Research Libraries' Office of Management Services (OMS), working with the Research Libraries Group, Inc. (RLG), began the North American Collections Inventory Project (NCIP) in July 1983 as a cooperative effort intended eventually to involve research libraries throughout the United States and Canada. The project's long-term goal is to develop an online North American inventory of research collections that can assist scholars in locating materials needed to support their research. Designed as a guide for libraries undertaking an interlibrary inventory or Conspectus-based collection assessment, this manual is divided into three parts. The first section provides an overview and serves as an orientation aid and ready reference tool for bibliographers and other collection development librarians. The second part covers the Conspectus methodology and procedures in detail and is intended to provide a handbook for planning, organizing, and carrying out the library's collection assessment within the framework of NCIP. This part also presents a brief history of NCIP and deals with issues and questions relating to the Conspectus methodology. The third part discusses four approaches to collection assessment: qualitative methods; quantitative methods; sampling methods; and list-checking methods. A variety of reference documents, examples, and statistical aids are appended. (MAB)