<p>Increasing environmental concerns demand the replacement of petroleum with renewable, sustainable resources to produce biodegradable and carbon-neutral products. As a natural, abundant and versatile biopolymer, cellulose has long been used in traditional applications such as paper and textiles and is now emerging in advanced fields including energy storage, healthcare, food, cosmetics, and paints and emulsions. Supramolecular chemistry offers a powerful strategy for engineering cellulose nanocomposites through specific, directional, tunable and reversible non-covalent interactions between nanocellulose and matrix components to achieve certain mechanical, chemical and biological properties. In this Review, we present the multiscale supramolecular engineering of cellulose nanocomposites and their fabrication and processing into materials. We provide a material and structural perspective of how the mechanical, ionic, optical and thermal properties and the environmental degradability of these nanocomposites can be regulated through supramolecular chemistry. Finally, we discuss how these approaches might address circularity and environmental sustainability goals, and we highlight major challenges and future prospects in the field, calling for further attention on supramolecular chemistry engineering to maximize the potential of these materials.</p>