Egg tempera is a painting technique that has been used for centuries. It is inexpensive and easy to learn. If done right, the final product can be amazing. The picture below is an example of the tempera technique on wood (by Niccolo Semiticolo, 1367).
The version I am going to outline in this instructable is what I was taught by my teacher in grad school. I have not tried comparing it to other tempera techniques. If you would like to learn some other ways of doing this, you can visit www.eggtempera.com
You can also find some history of egg tempera painting on Wikipedia