Optical Bonding is the affixing of two optical elements to one another using a liquid adhesive. The qualifier optical implies that the adhesive is transparent, has a suitable refractive index and is made under adequate control such that there are no significant variations in the optical properties within a single bond. In this way, we differentiate bonding from lamination.

On the practical side, the adhesive must also provide adequate bond strength, have a reasonable pot life after preparing, not present any health or safety issues, be available at reasonable cost from reliable sources, and cure to the proper finished bond condition using temperatures and times that are friendly to optical bonding facilities. Fortunately, there exist a relatively large number of choices. Typical bonded overlays include contrast enhancement filters, EMI/RFI filters, vandal shields, touch screens, and thermal heaters.