Life cycle assessment (LCA) is a comprehensive methodological framework for evaluating environmental impacts of products and processes throughout their entire life cycle. It can be used for many applications, such as identifying environmental impact hotspots of a product system, solution, and product comparison or marketing. The LCA process is divided into four phases: (1) goal and scope definition, (2) inventory analysis, (3) impact assessment, and (4) interpretation. The goal and scope definition answers to why and how the LCA will be conducted. The collected inventory forms the basis for the following impact assessment. In the end, the results are interpreted, and conclusions are made. In the evolving algae sector that moves from pilot-scale trials to complex biorefinery concepts, the role of LCAs is becoming ever more important as a key decision-support tool. However, for reliable, comparable, and useful LCAs, more common practices are needed. This chapter describes how to conduct an LCA for both micro- and macroalgae products while providing examples and describing common environmental impact hotspots.