Ninjas were stealth soldiers and mercenaries hired mostly by daimyōs. Their primary roles were those of espionage and sabotage, although assassinations were also attributed to ninja. The diverse range of skills practiced by the ninja is called ninjutsu - the art of stealth - and includes training in armed combat, weapon use, disguise, and infiltration. Some of the things that ninjas do include:

• Espionage: Espionage was the chief role of the ninja. With the aid of disguises, the ninja gathered information on enemy terrain and building specifications, as well as obtaining passwords and communiques.

• Sabotage: The ninja were skilled at sabotage, and would often use their abilities to disrupt enemy supply lines or destroy enemy fortifications.

• Assassination: Although not their primary role, assassinations were also attributed to ninja.

• Infiltration: The ninja were experts at infiltration, and could sneak into enemy territory undetected.

• Disguise: The ninja were skilled at disguising themselves, and could blend in with their surroundings to avoid detection.

• Combat: The ninja were trained in armed combat and weapon use, and were skilled fighters.

Ninjas did not always work alone, and teamwork techniques exist. For example, in order to scale a wall, a group of ninja may carry each other on their backs, or provide a human platform to assist an individual in reaching greater heights. The ninja were an important part of warfare and were even employed by the samurai themselves to carry out operations that were forbidden by bushidō.