This review covers the production, structure, properties and applications of nanowhiskers of cellulose. It is shown that these nanowhiskers can be generated, from various plant sources, with transverse dimensions as small as 3–30 nm, giving a high surface to volume ratio. Since the nanowhiskers are rod-like, it is shown how they can be self-assembled into chiral nematic liquid crystalline structures, not only in solution, but also in the dry state. The production of thin films of cellulose nanowhiskers, by spin coating and in combination with polymer electrolytes, is also covered. A wide range of chemical modification of cellulose nanowhiskers are reviewed; including 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation, polymerisation from the surface using Reversible Addition–Fragmentation chain Transfer (RAFT) and Atom Transfer Radical Polymerisation (ATRP), and the rendering of the surface with cationic and anionic charge. The mechanical properties of cellulose nanowhiskers will also be covered, including the measurement of their stiffness using both Raman spectroscopy and Atomic Force Microscopy (AFM) measurements. The final part of the review will cover the applications and potential industrial use of cellulose nanowhiskers; namely for nanocomposite materials, thin films and other applications. Finally, some conclusions, including perspectives and future developments will be presented.