This book highlights and explains some topics of functionalized, less common (e.g., bio-based) fibrous structures creation, characterization of their properties, and their special applications. It comprises mainly some important but not widely known fibers such as bacterial cellulose, coir, banana, and mohair fibers of natural origin, bio-based fibers, and waste-based fibers (such as paper), more suitable for the future needs of the textile branch. The benefits of the preparation of synthetic fibers from natural-based monomers in comparison with fibers of natural origin are shown. The use of reprocessed and recycled fibrous wastes, leading to a reduction of consumption of resources, whether renewable or fossil, is covered as well. The modification of fibrous structures by bio-prepared metal nanoparticles is also discussed.