Cellulose, a linear β-1,4-linked-homoglucan polymer, is the most abundant organic molecule in the biosphere and attracted fiber for an advanced functional materials. Cellulose-synthesizing organisms are widely distributed in biological kingdoms, ranging from Monera to Plantae and even to Animaria, tunicates. In this chapter, basic structure of cellulose microfibril and their diversity are reviewed in terms of crystalline allomorphism, cross-sectional shape, uniplanar orientation behavior and morphology of cellulose synthase complexes.