<p>The understanding of the interactions between cellulose and ionic liquids are the foundation for the development of new processes, to explore new reactions and to establish a circular bioeconomy. The main problem is that direct measurement, from both quantitative and qualitative point of view is challenging. While there are methods to assess solution strength and wettability of ionic liquids with cellulose materials, the main challenge lies in the combination of a solid substrate and an applied liquid, limiting the number of accessible methods. We demonstrate in this paper that an in-situ solid-state NMR spectroscopical&#xa0;approach is capable of monitoring in real-time the mobility of ionic liquids in cellulose-based substrates. Specifically, we employ ¹H → ¹³C cross polarization magic angle spinning (CP MAS) NMR spectroscopy to examine mobility changes over varying exposure times in paper samples treated with ionic liquids. Through this approach, we capture the temporal evolution of IL signals, which in turn provide insights into mobility changes of ILs and also allow for identifying changes in cellulose crystallinity. The approach allows for a simple, semiquantitative assessment of cellulose solubility in ionic liquids and is in principle applicable to other biomass materials as well.</p>