Ju-Jutsu, or better known as Ju-Jitsu, is a very old Japanese form of self-defense and attack.
In Japan, in the Middle Ages, the most powerful person was the Emperor. He had a very large territory to manage, therefore Japan was divided into relatively small parts and each part was assigned a Shogun. The Shogun was like a current governor. Both the Emperor and the Shoguns had their own armies: the Samurais.
A Samurai was a person, who was educated to become a soldier as a child and to be absolutely faithful to his Shogun and Emperor. If a Samurai received an order to kill himself, he executed it without blinking an eye! He was an expert killer with and without weapons. The most used weapons were swords (katana) and knives (tanto). At the same time they learned Ju-Jutsu, a very efficient martial art.
When the Emperor and the Shoguns were eliminated, the Samurai became unemployed and started travelling all over the land, teaching his know-how to everyone who was interested. Some of them started developing some different martial arts and founded their own schools. With the passing of time, each school developed its own kind of martial art and only the most interesting schools survived. In this way, a lot of sub branches (Karate, Aikido, Judo, ...) were born of which many still exist today.
Jigoro Kano (see http://www.judoinfo.com/kano4.htm) (1860-1938) founded Judo by removing all the dangerous techniques from Ju-Jitsu, so that all kinds of persons (children, seniors, women, ...) could practise Judo without injuring him- or herself.
Some people founded other forms such as Karate, which are concentrated hits (atemi) only.
An other person, Morihei Ueshiba (see http://www.renwakai.com/Version%20anglaise/histo.htm), founded Aikido, which is concentrated in the use of joints (wrists, elbow, shoulders, ...).
This means that the modern Ju-Jitsu uses the best techniques from other martial arts.
Today, Ju-Jitsu is taught all over the World. In Switzerland, the policemen must learn it during their training and it's strongly recommended that they continue practicing it later. Actually, in Switzerland, there aren't a lot of people interested in this sport and as a result the minimum age to learn it was reduced from 16 to 14 and then to 10 years.
Personally, I don't teach it to people younger than 16, because I think that children see enough violence in their lives without the need to learn how they can injure somebody.
The present name of this martial art that we use, is pronounced completely wrong. The people who first introduced it in the western part of the World stupidly started calling it Ju-Jitsu instead of Ju-Jutsu. Today, as a result, we only know this name, but if you speak with a Japanese, he has never heard this word.