Animal-based adhesives are natural glues made from animal products, primarily collagen, which is found in connective tissues like skin and bones. These adhesives have been used for centuries in various applications, including woodworking, bookbinding, and leatherworking. Common sources include hide glue, fish glue, and casein, a protein derived from milk. These adhesives are valued for their strong bonding properties and ability to be reactivated with heat or moisture. While they are less common in modern manufacturing due to the rise of synthetic alternatives, animal-based adhesives are still appreciated in traditional crafts and conservation work for their eco-friendly and biodegradable characteristics.