Abstract: Cellulose is the most widely spread organic polymer found in nature, since it constitutes the main component of the membrane of plant cell. The degree of knowledge on the structure of cellulose has evolved along with the progress made in the field of polymers, cellulose being the first macromolecular compound that was extensively studied during implementation and development of the concept of a macromolecule. Even though cellulose was isolated over 180 years ago, the study of this natural polymer has also remained at present of interest to scientists. The use of the X-rays diffraction method of investigation led to the observation that all native celluloses, no matter where they come from, display identical roentgenograms. These have been conventionally named by the term cellulose I. At the same time, based on X-ray diffraction studies, three other allomorphic forms have also been later identified: cellulose II – the mercerized cellulose or regenerated; cellulose III – the ammonia treated cellulose, and cellulose IV – the modified cellulose by thermal treatment. In all of these allomorphic states the molecular structure remains the same; what is modified is the network of hydrogen bonds developed at the neighboring and association limits of macromolecular chains, along with unit cell dimensions. The interconversions between the allomorphic structures of cellulose can be performed by the action of chemical reagents or thermal treatments. The polymorphism of cellulose always intrigued us through the non-elucidated aspects regarding both the obtaining and the structural organization of allomorphic forms.