Many methodologies have been developed which allow the user to respond in a substantive manner to NEPAregulations when preparing an EA/EIS document. Presented in this chapter is a review and analysis of some of these environmental assessment methodologies. The general categories of methodologies evolved quickly after the passage of NEPA, as researchers and practitioners sought to ensure that a systematic, interdisciplinary approach was used in preparing environmental documentation. The purpose of this discussion of assessment methodologies is (1) to acquaint the reader with the different general types of methodologies, and (2) to provide illustrative examples of available methodologies in each category. An initial review and analysis of assessment methodologies was first completed by Warner and Preston (1974). The discussion here draws substantially from their work. Other approaches, such as multiattribute utility theory, systems diagrams, and simulation modeling, provide alternative ways of grouping assessment methodologies. Some of these methodologies were reviewed by Bisset (1988). The Further Readings section provides references to still other approaches and organizational methodologies which may be of interest.