Ninjutsu (忍術), also called shinobi no jutsu (忍び術), is a collection of techniques originally practiced for espionage purposes. It includes methods of gathering information, non-detection, avoidance, and misdirection techniques. Ninjutsu can also involve training in disguise, escape, concealment, archery, medicine, and explosives.

Practitioners of ninjutsu have been seen as assassins for hire, and have been associated in the public imagination with other activities which are considered criminal by modern standards. Even though it was influenced by Chinese spying techniques and the strategic principles of Sun Tzu, ninjutsu is believed by its adherents to be of origin. One version is that the basis of ninjutsu was taught to a Japanese household who fled to the mountains after losing a battle. There they came across Chinese warrior monks who had fled China. Later, the skills were developed over 300 years to create ninjutsu.

Although the popular view is that ninjutsu is the art of secrecy or stealth, actual practitioners consider it to mean the art of enduring - enduring all of life's hardships. The character nin 忍 carries both these meanings, and others.

In the modern world the word ninjutsu usually refers to a certain system (Bujinkan Budo Taijutsu) of self defense, and its offshoots. It is true that ninjutsu has a long and myth-filled history, but today almost anyone is allowed to practice modern ninjutsu. As one makes progress in ninjutsu the system gets more sophisticated, and one might realize that the system contains more than fighting skills. To avoid misunderstandings, "ninjutsu" should just refer to a specific branch of Japanese martial arts, unless it is being used in a historical sense.

The 18 fundamental skills of the Togakure-ryū school of ninjutsu. (忍び術)

1. Seishin-teki kyōyō (spiritual refinement)
2. Taijutsu (unarmed combat)
3. Ninja ken (sword fighting)
4. Bōjutsu (stick and staff fighting)
5. Shurikenjutsu (throwing blades)
6. Sōjutsu (spear fighting)
7. Naginatajutsu (halberd fighting)
8. Kusarigama (chain and sickle weapon)
9. Kayakujutsu (fire and explosives)
10. Hensōjutsu (disguise and impersonation)
11. Shinobi-iri (stealth and infiltration methods)
12. Bajutsu (horsemanship)
13. Sui-ren (training in water)
14. Bōryaku (military strategy)
15. Chōhō (espionage)
16. Intonjutsu (escaping and concealment)
17. Tenmon (meteorology)
18. Chi-mon (geography)