Fusion is probably the most popular glass processing technique when it comes to art glass. Glass fusion implies glass melting, where two or more pieces of glass are heated together in a specialized furnace so as to be fused together. Glass softens at a temperature of 425℃ and melts at a temperature between 760℃ and 815℃.

The fusion technique is characterized by a wide range of processing possibilities and unique effects. It is possible to create different structures within the glass by adding different colors, combining several types of glass, working with irregular shapes and creating new shapes.

Glass heated to a lower temperature to create texture is called "tack fuse" and glass heated to a higher temperature to create a smoother finish is called "full fuse".