Travis picking is different from other styles of fingerpicking, it has a different sound, and requires different instrumental techniques---Mark's point is important! It is a way to play bass and melody at the same time--but you can fingerpick the melody with a bass line and still not be Travis picking-- The key element is that it has a strident bass line, with syncopated melody/lead figures played above it--

The style is played with thumb and index finger, only, and, it takes a long time to learn to do the business with the thumb that JP so accurately described above (I have to confess that a first I thought his description was off, but on close examination, it turns out that that is exactly what happens) and a while after that to be able to drop the top in--co-ordination and planning are critical, because if the arrangement doesn't fit together perfectly, it will wobble and fall apart--

I've been watching the Olympic Skating competitions, and it occurs to me that Travis picking is a lot like figure skating because practice is not enough to assure success, the performance depends on extreme focus and motivation-every mistake is very clear, and, because of the speed, errors in the transitions can be fatal--