What is impact assessment and why is it important?

Purpose - The purpose of this paper is to offer a definition of impact assessment and to discuss some of the implications of this and other definitions. A particular approach to impact assessment is introduced, as developed for use in a variety of library and information service settings and the principles underpinning this approach are described. Design/methodology/approach - This approach has been adapted by the Bill and Melinda Gates Foundation's Global Libraries Initiative (GL) when providing impact planning and assessment support to grantees through their "IPA Road Map". The approach is also adopted by the International Federation of Library Associations (IFLA) in devising its impact assessment strategy for evaluation of its future Free Access to Information and Freedom of Expression (FAIFE) work. Findings - The importance of impact assessment in a variety of settings is outlined: from school libraries to university researcher support and from public libraries to electronic information services. Research limitations/implications - Although this paper draws on and quotes from the IPA Road Map developed by the GL, all the comments and opinions expressed are those of the authors and should not be interpreted as representing an official GL viewpoint. Originality/value - Some "unofficial" observations are offered on the relationships between impact assessment, advocacy and service sustainability, particularly in relation to major service development programmes such as the GL.