Three main classes of glues are bone glue, hide or skin glue, and fish glue. Technically, gums and cements are not glues, but adhesives, as they are made from synthetic materials, but consumers tend to also call them glue.
Collagenous animal parts such as bones, hides, horns and hooves can be turned into hard gelatin and then "diluted" into glue. Starch-based glue, better known as paste, is made from carbohydrates extracted from plants. Mucilage is a polysaccharide extracted from plant roots and seeds. Epoxy is made from a class of synthetic thermosetting polymers containing epoxide groups.
A “glue” produced by mussels to help them stick to rocks underwater has been used to develop a new type of adhesive to perform repairs during surgery. Incorporating silver into the glue-like material can make it antibacterial.
Research shows that some glue chemicals affect cognitive abilities of the brain even 30 years after exposure (original study).