Swords were an integral part of samurai culture, but there wasn’t a single samurai sword. Swords in feudal Japan were adapted to the wielders and their targets. As warfare evolved and new enemies appeared, sword shapes changed accordingly.
Samurais used katanas and other Japanese swords. Before using katanas, they used tachi, which were longer and pointier. Over time, samurai started wearing a long and a short sword together. The pairing was called daisho. The long sword was a katana, and the short sword was a wakizashi or a tantō.
Katanas have an instantly recognizable shape. There was a lot of artistry behind the making of these swords, but there were also practical reasons for each of the design choices.
Also see Did Samurai Use Spears? to learn more.
What’s the Difference Between a Katana and Samurai Sword?
There isn’t a real difference between samurai swords and katanas. Katanas were one of the swords used by the samurai. However, samurai used different types of swords during their history. The tachi was the standard sword for samurai before katanas came into fashion.
Before the Katana
The Heian period saw the samurai rise to power. Starting as contracted warriors for independent landowners, samurai clans grew and eventually overthrew the imperial government.  They set up a military government in 1192 led by a shogun. The Emperor kept his title but had no real power.
This period coincides with the introduction of horses in battle. Horse riding completely changed the way samurais fought. They needed pointed weapons with enough reach to attack people on the floor. This is when long tachi swords became standardized among samurai.
The Rise of Katanas
In the following centuries, tactics started playing a more important role on the battlefield. Before, swords were designed for one-on-one duels. But during the Mongol invasions, Japan had to face highly organized and tactical enemies.
Japanese warriors and samurai needed a sword that allowed soldiers to remain mobile and organized. At the same time, horseback fighting became less common, and foot soldiers became the central part of an army.
The once-massive tachi was gradually shortened.  Some large tachi were made for battalion leaders, who still rode on horseback. These often surpassed 1 meter (3.3 feet) in length and could be as long as 1.5 meters (5 feet).
However, for most warriors and the usual dealings of samurai, a new, shorter kind of blade emerged: the uchigatana, which is equivalent to what people today call the katana. Uchigatana is the official name in Japan for this kind of sword, while katana is the word used by the Japanese for single-edged swords around the world.
Sometimes, katanas were made by shortening longer tachi. Both katanas and short tachi are usually measured around 70 cm (2.3 feet) in length.
There is actually very little difference between these two swords. The most notable one is how they’re held: katanas are held pointing up, while tachi are held pointing down. For this reason, the mei —the forging signature by the master blacksmith— were located in different places.
The Companion Swords
After the hectic Warring States period during the 14th and 15th centuries, a couple of centuries of relative peace followed. Samurai became more of an aristocratic class rather than clans of warriors, and their weapons became more ceremonial. 
During this period, it became the norm for samurai to carry two swords: a long sword —usually a katana or, less often, a tachi— and a companion short sword. This pairing was called daisho.
There were two types of short swords worn by samurai: the wakizashi and the tantō. The wakizashi measured between 30 and 60 cm (1 and 2 feet), while the tanto could measure under 30 cm (1 foot) and was closer to a dagger.
Katanas underwent many changes but never went beyond the 70 cm (2.3 feet) mark. Their final form took shape during the Edo period, and it’s the one people are most familiar with. It has an equal width across its length and a pronounced curve.
Also see Did Samurai Use Shields? to learn more.
How Did Samurai Use Katanas?
Samurai weiled their katanas with two hands and carried them with the edge facing up. Their primary purpose was cutting. Katanas were used in combat, but not as much as other weapons. In later periods, the main role of katanas was ceremonial. For samurai, carrying a katana was a symbol of status.
Katanas were seen as the extension of a samurai’s soul. Since childhood, samurai were taught Kenjutsu, the way of mastering swordsmanship. They learned different types of blows, proper footwork, and lightning-fast slashes.
Katanas were typically carried inside a sheath with the cutting edge facing up. Sometimes they would be carried without a sheath, but this could expose the samurai to self-injury.
This manner of carrying a sword was called buke-zukuri. It allowed samurai to draw their katanas in one quick, fluid motion. A samurai would point the sheath down, pull the katana slightly out with his left hand, and grip the hilt of the katana with his right hand as he slid it out.
Katanas were wielded with two hands, with the top of the sword pointing upwards. Their curved blade was optimal for cutting, but its point also allowed for stabbing movements. Katanas were used in battle, while the wakizashi was used for close-quarters combat and self-defense.
However, it’s debatable how much katanas were actually used in warfare. Other weapons like bows and spears were more common and perhaps more effective.
Also see Did Samurai Kill Civilians? to learn more.
Can People Buy Authentic Katanas Today?
People can buy authentic katanas today. New authentic katanas can cost from $200 to $500. Antique or premium katanas by renowned blacksmiths can cost tens of thousands of dollars. If bought from a legal seller in Japan, the sword can be legally shipped overseas.
Owning a katana is legal in most parts of the world. The Samurai Museum in Japan reportedly exports katanas across the world without an issue.  However, some countries’ customs can potentially create trouble. Buyers should check if there are any restrictions on transporting sharp objects where they live.
Authentic katanas have a soft, low-carbon steel core surrounded by hard, high-carbon steel. This ancient technique gives katanas their unique flexibility and durability.
Also see Did Samurai Use Axes to Fight? to learn more.
The katana wasn’t just a warfare tool. During the Edo period, when it became a samurai’s staple weapon, katanas had huge ceremonial importance.