Cellulose is one of the most abundant biopolymers on earth. It is a sustainable and renewable raw material with many beneficial properties. Due to its availability, nontoxicity, environmental friendliness, biocompatibility, and biodegradability, cellulose is one of the world's most used biopolymers. Cellulose is currently establishing its role as a strong potential candidate for advanced applications in various engineering fields. In addition, cellulose and some of its derivatives exhibit properties, which recommend themselves for use in optical applications and for manipulating light in a targeted manner. In the last decades, efforts were directed toward the production of artificial ordered structures such as photonic crystals, chiral nematic liquid crystals or Bragg stacks, as well as disordered structures such as random lasers from cellulose in order to tailor the interaction of visible light with biopolymers. Due to its sustainable availability and its ability to manage light interactions, cellulose is increasingly used in optoelectronic devices to replace fossil‐based polymers. Cellulose and its derivatives can be consequently applied as optical fibers, probes, organic light emitting diodes, flexible touch screens, and solar cells. The present review provides an overview of the processability and applications of cellulose and its derivatives for the specific manipulation of light.

Disorder and photonics have long been seen as natural adversaries and designers of optical systems have often driven systems to perfection by minimizing deviations from the ideal design. Especially in the field of photonic crystals and metamaterials but also for optical circuits, disorder has been avoided as a nuisance for many years. However, starting from the very robust structural colors found in nature, scientists learn to analyze and tailor disorder to achieve functionalities beyond what is possible with perfectly ordered or ideal systems alone. This review article covers theoretical and materials aspects of tailored disorder as well as experimental results. Furthermore selected examples are highlighted in greater detail, for which the intentional use of disorder adds additional functionality or provides novel functionality impossible without disorder.