Product life cycle assessment (LCA) is an attractive tool for making environmentally-informed choices from among product alternatives. The results of an LCA – the product’s ‘environmental profile’ – is essentially a list of the product’s direct or indirect contributions to various kinds of environmental impact, such as climate change, acidification, eutrophication, toxicity, land use and resource depletion. Before a choice can ultimately be made, it is important that the various environmental impacts are made mutually comparable, enabling the impact scores for each product alternative to be translated into a one-figure final score. For this ‘weighting’ step in LCA a variety of methods have been developed. It is a controversial issue, though, because in this kind of procedure value judgments are by definition inescapable. This report discusses the main LCA weighting methods available and the pros and cons of weighting in the LCA context.