The pulp and paper industry, based on the plant cell wall component cellulose, is an economic mainstay in many countries. Although cellulose, this “old”, long-established and well-researched biopolymer, does not seem to offer any major scientific challenges anymore at first glance, research continues to uncover new, astonishing facts and remaining mysteries. Some recent cases are all related to different aspects of the system “cellulose – water”. For example, the surface of nano-structured celluloses offers a peculiar reactivity which the surface-confined water representing a separate phase with a reactivity very different from bulk water. This can be exploited for reliable, regiospecific modification (only surface, only OH-6) of celluloses. Second, the solid-state transition from cellulose I to cellulose II in the presence of strong alkali (mercerization) involves a chemical transport process that occurs only within a very narrow window for the surface water and NaOH concentration. Third, most carbonyl functions (aldehydes, ketones) in cellulosics are not present in their conventional forms, but as masked species, such as hydrates, hemiacetals or hemialdals. This is of central importance in the chemistry and analysis of oxidized cellulosics, for instance upon periodate oxidation or in bleaching and chromophore chemistry. In all these example cases, water obviously plays a crucial role which, however, is far from being fully understood. 
The presentation will address some of the latest findings on various aspects of the system “cellulose – water”, discuss different views, highlight open questions, and emphasize how fascinating cellulose science continues to be.