It has been mentioned in Chapter 12 that Life Cycle Assessment (or LCA) is one of the analytical instruments within the toolbox for analyzing the interface of economy and environment. This section provides a worked example of the LCA technique. It is a fairly elaborate demonstration of a quite simple hypothetical product system. No real case study and data were chosen, the reason being that the number of data items would be too large to be sorted out in an educational setting. All data are therefore fi ctional and no claims should be made with respect to the results of the exercise. With respect to the methods that are presented, a similar though weaker statement must be made. There is not one unique interpretation and implementation of the principles of LCA, and any attempt to illustrate LCA by means of a concrete example should be understood as an illustration indeed. The purpose of this section is therefore to point out the main idea and methodological principles of LCA by means of a hypothetical example with fi ctitious data. In doing so, we will concentrate on the computational content of LCA. Of course, the entire concept of LCA embraces (or: may embrace) many types of activities and aspects, including involvement of stakeholders, collecting of data, verifi cation of data, manipulation of data, and carrying out peer reviews. To what extent stakeholders play a role and how this role should be embedded is something that not only is under discussion, but which also varies from situation to situation. The same applies to the process of peer review. Obtaining and verifying data are cumbersome activities which require a good deal of process-technological and ecological and toxicological knowledge. In contrast, the recipes that are used to manipulate the data are of an almost mechanical nature. There is not much disagreement (although at some places there is some). Strangely enough, almost all textbooks discuss those parts that are diffi cult and controversial, while the more or less rigorous basis is often left out of consideration. We feel, however, that a presentation of these basic mechanisms of the method for LCA is indispensable for a proper understanding of the meaning of the results of an LCA.