This chapter summarizes the research on how non-wood lignin is processed for polyurethane use, including its chemical properties, synthesis pathways, environmental effects, and economic opportunities. The goal is to assess how this abundant bio-based polymer can mitigate barriers to establishing sustainable replacements for petroleum-based polyurethanes. Evidence suggests various chemical modifications such as phenolation and oxypropylation can improve lignin’s reactivity and compatibility, resulting in improved mechanical properties and thermal stability in polyurethane formulations. Along with these chemical modifications, new synthesis methods, such as non-isocyanate and solvent-free methods, hold clear environmental advantages and can offer pathways toward recyclability. However, they are limited in terms of scalability and complexity of synthesis. Environmental assessments indicate that lignin-based polyurethanes can lead to moderate reductions in carbon footprint and increase biodegradability, but these benefits may be compromised by both the impact of energy demands and chemical inputs associated with processing for sustainability. Cost competitiveness is possible, but that will rely on a more consistent feedstock quality and efficient production methods. At the same time, application studies have shown promising results: lignin-based polyurethanes performed well in foams, elastomers, coatings, and adhesives, with some providing extra benefits like ultraviolet (UV) resistance and self-healing properties. In sum, these results suggest non-wood lignin polyurethane demonstrates potential as a path toward sustainable solution materials. However, significant additional work will be needed to understand the commercial potential of non-wood lignin polyurethanes, especially when it involves scaling production, working through lifecycle analysis, and commercializing these products.