Adhesive, also known as glue, cement, glue or paste, refers to any non-metallic substance applied to one or both surfaces of two separate projects, which binds them together and prevents them from separating. Adjectives may be used in conjunction with the term "adhesive" to describe the physical or chemical form of the substance, the type of material connected or the nature of the conditions of use.

The use of adhesives has many advantages over other bonding technologies such as sewing, mechanical fixation, and thermal bonding. These adhesives include the ability to bond different materials together to distribute stress more effectively across the joint, the cost-effectiveness of easy to mechanize processes, improvements in appearance design, and increased design flexibility. Disadvantages of using adhesives include reduced stability at high temperatures, relatively weak adhesion of large objects with a smaller bonding surface area, and greater difficulty in separating objects during testing. Adhesives are usually organized by bonding. They are then organized into reactive and non reactive adhesives, which means whether or not the adhesives react chemically to harden them. Alternatively, they can be organized by whether the raw materials are natural or synthetic sources, or by their initial physical stages.

Adhesives can be natural or synthetic. The earliest human use of binders was 200000 years ago, when Neanderthals produced tar from the distillation of birch bark, which was used to bond stone tools to wooden handles. The first mention of adhesives in the literature was in 2000 BC. The Greeks and Romans made great contributions to the development of adhesives. In Europe, glue was not widely used until 1500-1700 A.D. From then on until the 1900s, the use of adhesives was increasing and found to be relatively gradual. Until the last century, the development of synthetic adhesives has accelerated rapidly, and the innovation in this field has continued to the present.