Iaido primarily uses a traditional Japanese sword known as a "katana" for its practice. The katana is a curved, single-edged sword with a long grip that allows for a two-handed grip. It is the iconic weapon associated with samurai warriors and has a rich history and cultural significance in Japan.

The katana used in iaido practice is generally an unsharpened training sword called an "iaito." The iaito is specifically designed for safe and effective practice, replicating the weight and balance of a real katana while having a blunt or rounded edge to ensure safety during training. The iaito allows practitioners to perform the intricate drawing, cutting, and resheathing techniques of iaido without the risk of accidental injury.

It's important to note that while the majority of iaido practitioners use the katana/iaito, there are also other traditional Japanese swords used in specific styles or schools of iaido. These include the wakizashi (a shorter companion sword to the katana) and the tanto (a shorter, single-edged knife-like sword). The specific sword used can vary depending on the iaido style or school being practiced.