This book provides research on the synthesis and applications of polymer nanocomposites. Chapter One discusses advances in injection moulding technology of polymer nanocomposites. Chapter Two reviews the functionalisation and applications of carbon/polymer nanocomposite (bio)sensors containing nanoparticles. Chapter Three focuses on polymer composites based on highly anisotropic cellulose nanocrystals. Chapter Four studies a novel nanocomposite specifically developed for chemical treatment of walls, floor, ceiling, roof, etc., to prevent or limit exposure to dangerous gases seeping into buildings through constructive materials.