In 9th - 12th Century Japan, great houses and the samurai ruled. The great houses fueded and sought advantage by any means possible byt the samurai were goverened by the Bushido, the warrior way of honor, which prevented them from assisination and gathering information from within another's house so the ninja was born.

The ninja did not have the strength or training of the samurai but myths spread of Ninjas ability to become invisible, turn into animals, etc. and the ninja fostered and capitalized on these myths. The ninjas only objective was to get the job done and they invented weapons, clothes and techniques to allow them to succeed.

Techniques

Ninja Training Academies and Campls

Equipment

Ninja weapons

Ninja swords

Fantasy swords

Samurai swords

Miscellaneous

School Listing
There aren't many traditional ninjitsu dojos but you can find many here.