Natural fibers' abundance, excellent properties, biodegradability, and low cost make this renewable resource a green alternative to synthetic fibers for composite material reinforcement. The need to create sustainable solutions has promoted applications in sports, transportation, armor, medicine, infrastructure, construction and building materials, and architecture. This collection promotes the use of natural materials and their composites as a possible strategy to increase environmental sustainability, as well as to study materials fundamentals for new applications. Topics include but are not limited to: