Watch the The Travis Picking Technique online guitar lesson by TrueFire from Acoustic Guitar Greatest Hits Vol. 2
Lesson Source: David Blacker's Lone Wolf Blues
The Travis picking technique has its roots in early blues music (probably way before) and was made famous by Merle Travis. You can also hear it in players like Chet Atkins, Brian Setzer, Scotty Moore, and many more.
The idea here is that you alternate a bass line between two of the low strings played with the thumb of your right hand. While you're keeping the bass line going you embellish it with melody notes on the top strings.
Here in this video we look at a really simple example of Travis picking over G and C chords. If you are new to this then practice it one beat at a time until it becomes natural. When you think you have it pretty solid then try to work with the play-along.