Harmonica/Basic Chords

All diatonics, tremolo, and chromatics are capable of true chords (i.e. all the notes sounded at the same time); however, the chords may not be appropriate for the music you are playing.

Diatonics are specifically designed with chording in mind, and such, it lacks the 4th, 6th, and 7th notes in the bottom octave. As such, the chords available are the following: European Tremolos also have the same number of chords available.
 * Straight harp:
 * I chord, all on blows holes 1-3, 4-6, 7-9.
 * ii chord, on draw hole 4-6
 * V chord, on draw hole 2-4
 * V7 chord, on draw hole 2-5
 * vii° chord, on draw hole 3-5
 * Cross harp:
 * I chord, on draw hole 2-4
 * I7 chord, on draw hole 2-5
 * iii° chord, on draw hole 3-5
 * IV chord, all on blows holes 1-3, 4-6, 7-9.
 * v chord, on draw hole 4-6
 * Third position
 * I-major on draw hole 4-6
 * IV-major on draw hole 2-4

Chromatics, which usually is played in the key of C, have the following chords available: East Asian Tremolos also have the same number of chords available.
 * I chord, all on blow hole 1-3, 5-7, 9-11
 * ii chord, all on draw hole 1-3, 5-7, 9-11
 * vii7-minor chord, all on draw hole 4-7 and 8-11

Of course, one can attempt to bring about more chords with bending techniques; this is especially common in cross-harp playing.