Watch the Harmonics Overview online guitar lesson by Muriel Anderson from 50 Right-Hand Techniques You Must Know
Harmonics are a great way to get very high notes, or to add a high shimmering sound to your music. By understanding a little about the physics and mechanics behind the technique, you can create a variety of effects and even find your own ways to play harmonics.
When you very lightly touch the halfway point of the string (at the 12th fret or 12 frets above whatever note you are playing) it will ring an octave higher than the original note (the fundamental). You can also touch at the 1/3 point of the string* (7 frets above the fretted note) to get an octave and a fifth above the original note, or the 1/4 point of the string (5 frets above the fretted note) to get two octaves above the original note.
It is interesting to note that besides the octave, the interval that occurs with the simplest string ratio is the interval of the fifth - the primary building block of much of our music. You can pluck on either side of the harmonic node with any finger. In my arrangement of Silent Night (available on the sheet music page of my website) I use 19 different harmonic techniques.