A soldering iron is a tool used for applying heat to two adjoining metal parts such that solder may melt and flow between those parts, binding them securely and conductively.

A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing a current, supplied through an electrical cord or a battery, through a heating element. Another heating method includes combustion of a suitable gas, which can either be delivered through a tank mounted on the iron (flameless), or through an external flame.

Some soldering irons heat up and cool down in a few seconds, but others take minutes.