**Abstract**

Increased consumer awareness and new regulations about climate change accelerated the need for solid, provable, transparent actions leading to results to support the sustainability claims and initiatives of fashion brands. However, progress on transparency is still very limited despite the alarming signals of climate change. As stated in Fashion Revolution's Transparency Index 2023, brands have achieved an overall average score of 24%, up 1% from last year. Transparency is a tool for transformation. A productive conversation toward the targets can only start with a certain level of transparency to lead to the desired change. Life cycle assessment (LCA) methodology represents the next level of transparency. LCA can help brands collect, analyze and monitor their sustainability performance with science-based results. It is a tool that is used to quantify the environmental performance of a product taking the complete life cycle into account (from raw material production to transport, fabric production, garment manufacturing, consumer use, and final disposal. This book chapter focuses on how brands can use LCA as a transparency tool, its advantages and challenges in generalizing the science-based data. A framework will be generated on how to build the LCA model and use the data to compare different products and production practices in denim industry.

**Keywords:** life cycle assessment, transparency, denim, environmental impact categories, sustainability, emissions
