Judo was first invented in 1882 by a Japanese man called Jigoro Kano. From its beginnings in Japan, judo has become a very popular sport all round the world and is now an Olympic sport. Judo is a way of defending yourself and is a very popular form of self-defence because even a small person can win a fight against a bigger one.
You might like to look at the book Judo to discover some of the techniques on learning this sport. Perhaps you can join a club. Maybe we will even see you at the Olympics.