Sword making, historically, has been the work of specialized smiths or metalworkers called bladesmiths or swordsmiths. Swords have been made of different materials over the centuries, with a variety of tools and techniques. While there are many criteria for evaluating a sword, generally the four key criteria are hardness, strength, flexibility and balance. Early swords were made of copper, which bends easily. Bronze swords were stronger; by varying the amount of tin in the alloy, a smith could make various parts of the sword harder or tougher to suit the demands of combat service. The Roman gladius was an early example of swords forged from blooms of steel.

A good sword has to be hard enough to hold an edge along a length which can range from 18 in (46 cm) to more than 36 in (91 cm). At the same time, it must be strong enough and flexible enough that it can absorb massive shocks at just about any point along its length and not crack or break. Finally, it should be balanced along its length so that it can be wielded effectively.