In the millions of years of evolution, nature has developed very efficient systems that move all elements and substances in cycles so that there is no waste. Humans, on the other hand, have recently developed industrial systems in the last few centuries that have a linear flow, extracting resources from nature and discarding them as waste after a brief period of use. Solutions to handle pollution have moved from end-of-pipe treatment to cleaner production and now towards a circular economy. A circular economy tries to move away from this linear model in trying to extend the life of products and services while minimizing burdens to the environment. To ensure that there are actually environmental benefits, a life cycle thinking approach is essential. This philosophy is developed in the chapter and life cycle assessment is introduced as an essential tool for environmental evaluation. Case studies on sugarcane biorefinery and packaging materials are provided to illustrate the utility of life cycle assessment in ensuring environmental benefits when approaching circularity.