The position of the thumb is important in left hand technique.

When playing a nylon string or classical-type guitar, the thumb of the left hand should move along the center and top of the back of the neck (see left illustration). It may be placed slightly higher on the neck of a steel string guitar (see right illustration).

Nylon (left) and steel (right) hand positions

My students frequently make the mistake of playing with the left hand thumb position way too high. This becomes a real problem later when we study bar chords (or barre chords) and when we need to improve left hand reach. You’ll want to arch your fingers up and over the strings, you can't do that if your left hand thumb rides too high up on the back of the guitar neck.

The guidelines presented here are for right-handed players. If you are left handed simply reverse them.

Next up: Basic Right Hand Position