Needs assessment is a fundamental part of evaluation, and yet it has not developed as rapidly in sophistication as other evaluation methodologies. This is largely due to the difficulty in measuring real needs, as opposed to wants, interests, etc. This paper discusses some of the critical issues in needs assessment, and outlines some of the fundamental questions that must be answered in order to design a valid and reliable needs assessment study. Emphasis is placed on the need for considering resources and constraints in designing a realistic approach to needs assessment. (Author)