The following document provides an introductory overview of Life Cycle Assessment (LCA) and describes the general uses and major components of LCA. This document is an update and merger of two previous EPA documents on LCA (“Life Cycle Assessment: Inventory Guidelines and Principles,” EPA/600/R-92/245, and “LCA101” from the LCAccess, website, http://www.epa.gov/ORD/NRMRL/lcaccess). It presents the four basic stages of conducting an LCA: goal and scope definition, inventory analysis, impact assessment, and improvement analysis. The major stages in an LCA study are raw material acquisition, materials manufacture, production, use/reuse/maintenance, and waste management. The system boundaries, assumptions, and conventions to be addressed in each stage are presented. This document is designed to be an educational tool for someone who wants to learn the basics of LCA, how to conduct an LCA, or how to manage someone conducting an LCA. Companies, federal facilities, industry organizations, or academia can benefit from learning how to incorporate environmental performance based on the life cycle concept into their decision-making processes. This report was submitted in fulfillment of contract 68-C02-067 by Scientific Applications International Corporation (SAIC) under the sponsorship of the United States Environmental Protection Agency. This report covers a period from December 2005 to May 2006, and work was completed as of May 30, 2006.