This book clarifies a number of methodological issues in Life Cycle Inventory modelling, as part of LCA. Some of these issues have been on the agenda for a long time, without coming to generally accepted solutions, and often not even to agreement on alternative approaches. Several of these subjects relate to the specific nature of LCA as a relatively simple method for decision support, focusing on technology relations in the life cycle. By this focus, it is simple enough to be operable by 'small' users, but at the cost of leaving out many mechanism which are operant in reality. The report before you has three main chapters: Chapter 1 gives a survey of issues in LCA which need further elaboration, and indicates priorities. Chapter 2 is about current LCA and how it may advance in terms of a number of methods issues: Multifunctionality; prospective and descriptive analysis in LCA; and data quality, uncertainty and validation. Chapter 3 is about how sustainability analysis might advance, not within the current limitations of ISO LCA. This chapter may function as a framework for improving sustainability analysis: as broadened and deepened LCA, as 'New LCA' or 'beyond LCA'.