Ninjutsu literally means "stealth technique". Ninjutsu is the heading name for traditional Japanese schools of fighting arts which have been created in the Japanese provinces Iga or Koga. These lands, rough and dominated by mountains, were places of refuge for refugees, hermits, lordless samurai (ronin) and religious minorities. To defend themselves and their families they developed unique fighting techniques, which later on became different fighting styles. During these times the specialized assasins known as ninja used advanced ninjutsu techniques in their stealth attacks. At one period of time there existed more than 70 different schools, and often only the elite members of family clans trained students at the multiple schools. Only a few schools of teachings in certain ninjutsu-based fighting styles reached the modern day. These remaining schools were taught by Takamatsu Sensei, the former Soke, to his successor Masaaki Hatsumi and are now trained in the Bujinkan Ninjutsu System. (Most other Ninjutsu schools in the world today come from this line. The others probably died out.)

Additional information on wikipedia