Harmonics are a natural feature of vibrating objects. For string instruments like the guitar, harmonics are played by lightly touching a string at certain places to mute the fundamental pitch (the note you ear when you play an open string), but still allowing the overtones of the string to sound. The loudest harmonics occur at the 12th, 7th and 5th frets and correspond to the 1/2, 1/3 and 1/4 divisions of the string. Harmonics played with an open string are called natural harmonics, when played with a fretted string, they are called artificial harmonics. The chart below shows where to find the harmonics on each string and how they might be notated. There really isn’t a standard way to notate harmonics, and things can get particularly confusing with artificial harmonics, so you may encounter different notation systems from time to time.
Here is an interesting Harmonic Study for two guitars that uses all of the harmonics on the 12th and 7th frets (plus one on the 5th fret!). Looking for an additional challenge? Try playing both parts by yourself!
(Please consider supporting this site! Sheet music and tablature for Harmonics Study for Two Guitars and Harmonics Study for Solo Guitar and other guitar studies available here: Innovative Studies for Guitar – Volume 2)