Cellulose dissolution is the disruption of the hydrogen-bond network that holds glucan chains in crystalline microfibrils, so that the chains disperse as individual molecules in a liquid medium ^[1]. Intramolecular bonds stiffen each chain while intermolecular bonds stack neighbouring chains into sheets, and a solvent must break both without derivatising the hydroxyl groups ^[1]. Effective media pair a hydrogen-bond acceptor with a cation or a base, among them aqueous alkali-urea, N-methylmorpholine-N-oxide, ionic liquids and deep eutectic mixtures ^[2]. Dissolution is distinct from swelling, in which the network loosens while crystalline order survives, and from derivatisation, which alters the chain chemistry ^[3]. Recovery of the polymer from solution regenerates the cellulose II polymorph rather than the native form ^[3].