An adhesive is any substance that makes things stick together. When you use glue to attach paper to cardboard, squeeze a tube of super glue to fix a broken toy, or peel the backing off a sticker, you're working with adhesives.

Different adhesives work in different ways and have different strengths. School glue washes off easily with water, which is perfect for art projects but useless for repairing a ceramic mug. Epoxy creates bonds so strong they can hold metal parts together in bridges and airplanes. Double-sided tape uses a mild adhesive that lets you reposition things, while permanent mounting tape creates a bond that's nearly impossible to break.

Scientists and engineers constantly develop new adhesives for specific jobs. Some adhesives work underwater. Others can withstand extreme heat or cold. Medical adhesives help close wounds without stitches. Adhesive can work as an adjective too: an adhesive bandage is a bandage with a sticky backing that holds it to your skin.

The right adhesive for any job depends on what you're sticking together, how strong the bond needs to be, and whether you might want to take it apart later.