Bionanocomposites are an emerging class of hybrid materials derived from combination at the nanometric level of inorganic solids with biopolymers. Certain biological materials, eg, nacre, ivory, bone and tooth, can be considered natural occurring bionanocomposites. The combination of polysaccharides, proteins, nucleic acids, and other biological materials with clay minerals, silica, phosphates, carbonates, and other inorganic solids opens the way to the preparation of a vast amount of bionanocomposites. Just like conventional nanocomposites, these biohybrid materials also exhibit both structural and functional properties, which can be of great interest for different applications. The most salient properties of bionanocomposites are related to biocompatibility, biodegradability, and good mechanical properties. These properties are of great significance in their application to regenerative medicine and in the development of environmentally friendly materials (green nanocomposites). Other examples of their potential application concern food packaging, fire safety, and sensor devices, which are based on gas‐barrier, flame retardancy, and sensing properties of bionanocomposites, respectively.