Native cellulose is a structural material that is biosynthesised as microfibrils by a number of living organisms ranging from higher and lower plants, to some amoebae, sea animals, bacteria and fungi. The chemical modification of cellulose microfibrils is investigated for preparing new bio-based materials with end-use properties in the fields of adhesion, textile, detergent, paint, cosmetic, medicine, food, etc. This book highlights the methods of preparing the cellulose conjugates which can be water-soluble materials or water-insoluble materials, to identify linkage with carboxylated cellulose materials through amide bonds and to understand the obtained results following by FT-IR, NMR spectroscopies (at liquid and solid states) and electron paramagnetic resonance spectroscopy.