This book is based on doctoral research, portrays the various approaches of utilizing cellulose, in three parts. The first part is on utilizing cellulose fibers as reinforcing materials. It is focused on the effect of fiber treatment on material properties and their durability under biotic/abiotic conditions. It was purported that for various applications of natural fiber reinforced composites, the treatments on the fiber have to be optimized depending on their durability requirement. Then it discusses the possibilities of incorporating both nanoparticles and cellulose (micro)fiber in thermoplastics. The strategy of improving properties of starch matrix is also revealed by fiber- reinforcement and photo-induced-crosslinking. The second part is on utilizing cellulose esters and portrays the preparation and characterization of nanocomposites of clay and polyethylene-glycol- /lactide-grafted- cellulose esters. They are found to exhibit various structural morphology and mechanical properties depending on the preparation methodologies involved. Third part discusses the synthesis of nanoscale hydroxyapatite using a cellulose derivative.