sometimes used interchangeably with the term ninpō is the martial art, strategy, and tactics of unconventional warfare and guerrilla warfare practiced by the shinobi (commonly known outside of Japan as ninja). A female ninja is called a Kunoichi.

While there are several styles of modern ninjutsu, not all can be related to the historic practice of ninjutsu in Japan so as to be considered a koryū.

Ninjutsu is the most feared forms of Martial Art because there is a lot of mystery attached to it. The disciples of this Japanese Martial art are known as Ninja and they learn the various techniques of survival, which is at the core of the Martial art.

The Ninjutsu training is one of the toughest and revolves around mastering the techniques of disguise, concealment, sword fighting, explosives, medicine and gathering information. This is a Martial art of endurance and consists of 18 different skills from spiritual refinement to throwing stars (shuriken) and using the famous Samurai Katana sword.

In Japanese "Ninja Jūhakkei" the eighteen disciplines (jūhakkei < jūhachi-kei) were first stated in the scrolls of Togakure-ryū. Subsequently they became definitive for all ninjutsu schools by providing total training of the warrior in various fighting arts and disciplines.

Ninja jūhakkei was often studied along with Bugei Jūhappan (the "18 samurai fighting art skills"). Though some are used in the same way by both samurai and ninja, other techniques were used differently by the two groups.

The 18 disciplines are:

   1. Seishin-teki kyōyō (spiritual refinement)
   2. Taijutsu (unarmed combat, using one's body as the only weapon)
   3. Kenjutsu (sword fighting)
   4. Bōjutsu (stick and staff fighting)
   5. Shurikenjutsu (throwing shuriken)
   6. Sōjutsu (spear fighting)
   7. Naginatajutsu (naginata fighting)
   8. Kusarigamajutsu (kusarigama fighting)
   9. Kayakujutsu (pyrotechnics and explosives)
  10. Hensōjutsu (disguise and impersonation)
  11. Shinobi-iri (stealth and entering methods)
  12. Bajutsu (horsemanship)
  13. Sui-ren (water training)
  14. Bōryaku (tactic)
  15. Chōhō (espionage)
  16. Intonjutsu (escaping and concealment)
  17. Tenmon (meteorology)
  18. Chi-mon (geography)

Today the main focus of ninjutsu deals with the techniques relevant to armed and unarmed combat

The greatest Ninja fighter is Dr. Masaaki Hatsumi also known as the Soke or Grandmaster.