Hi, my name is Marcus Milius. I play harmonica. I got a degree at the University of Southern California, a Bachelor's of Music, in Jazz Studies - Chromatic Harmonica. I play and teach harmonica here in New York City, and I'm happy to show you what I do. So playing the harmonica in the key of C is really simple when you're playing the diatonic harmonic. Because it's a diatonic harmonica it's set up in one key. So simply you need a diatonic harmonica in the key of C. If you just pick up the harmonica and just play anywhere you will be playing in the key of C. Whether you're playing chords or single notes - anywhere you play on the harmonica, you'll be in the key of C. The only thing you need to make sure is that whatever component you use, that that's in the key of C as well. So if you're playing along to a recording, you want to find out the key of that recording and make sure it's in the key of C. If you use the wrong key harmonica, you will not be in the key of C. There are ways to do that, but typically the harmonica is setup to play in one key. That is called playing in first position, also known as straight harp - and done by artists like Bob Dylan and it's a very cordial kind of style. However, you can play in all twelve keys on a C harmonica. It just becomes more difficult. The easiest key would be first position, and then second position, third position - twelve different positions, because there are twelve different keys. So, you could technically play in the key of C on any other tuned harmonica like an A harmonica or a G harmonica or an F harmonica. But it becomes a little more difficult. You have to choose your notes and use advanced techniques like bending and over-blowing to make sure you stay in the scale. A little harmonica in C major in first position. You can play single notes, or chords - anything works anywhere on the harmonica. And if you played with chords.