Cellulose is a natural fibrous carbohydrate, is the main structural element of plant cell walls, and is the most abundant natural polymer found in the biosphere. Due to its abundance and chemical stability, it has been used as a raw material in various industries for thousands of years. Due to developments in nanotechnology, materials that are used in macroscale abundantly are also utilized for nanomaterial design, and cellulose‐based nanomaterials have gained more interest in recent years. The unique properties of cellulose‐based nanomaterials including their chemical stability, high degree of crystallinity, biocompatibility, biodegradability, and tunability of their chemical (e.g., surface modification) and physical (e.g., shape) properties make them good candidates for functional nanomaterial design. This review brings advances in cellulose‐based nanomaterials for application in two major fields, sustainability and therapeutics.