When most people think of soldering, a soldering iron is the first tool that comes to mind. However, this is only one tool to accomplish the task.
Soldering torches were the first innovation in soldering. They work very similarly to welding torches, albeit with gases that burn at a much lower temperature. They can offer an impressive degree of control, but they are also quite expensive to maintain and fuel, compared to electric soldering solutions. Soldering torches are also the most difficult soldering tool to master, and are usually only used for very specialized tasks in modern times, or by individuals using them for artistic purposes.
Soldering irons are the most common tools for soldering. These are also the most accessible and inexpensive tools for the job, and are commonly used in classes for electronics and metalwork. They use an induction heating element to heat the work and allow solder to flow. However, soldering irons are bulky, and relatively unsuitable for fine work. As a consequence, they are becoming depreciated for professional ends.
Resistance soldering is the most recent innovation in soldering technology, though it has been around long enough that it is well-understood and mastered. While the initial investment is expensive, they offer the most precise control of all soldering methods, making them a popular choice for professionals, as well as for amateurs who wish to improve their craft in soldering. They are growing more inexpensive as time wears on, making them much easier to budget for electronics enthusiasts and shop-owners alike.