When considering substitution of materials and products that cannot be eliminated or re-designed for reuse, it is key to avoid regrettable substitutions. Based on systems thinking and life cycle approaches, this topic sheet provides guidance to identify trade-offs and prevent burden shifting when substituting materials or products in the market. It draws upon key learnings from the Life Cycle Assessment (LCA) meta-studies developed by UNEP and the Life Cycle Initiative on single-use plastic products and their alternatives.