The chromatic harmonica has a button on the side which allows you to play the normal major scale, and with the button depressed, gives you all the half steps or notes in between.

This allows you to play any scale, in any key, but you can't bend notes very well on this instrument so you don't get the same "bluesy" sound as on the diatonic.

Reading music and song tab for the chromatic- The chromatic harmonica hole layout is similar (sometimes referred to as "Solo" tuning) to the diatonic hole layout (referred to as "Richter" tuning), but not the same, so song tablature is different.

Many accomplished chromatic players are able to read standard music notation which eliminates the need for song tab.

The chromatic is mostly used for jazz, classical, and pop music- The chromatic harmonica is typically used in jazz, classical, pop, and music where the melodies require more than a 7-note scale (like the one on a standard diatonic).

A classic example of where a chromatic would be required is the theme song to "Midnight Cowboy". The original theme to "Sesame Street" was also played on a chromatic.

People who play the chromatic harmonica- Stevie Wonder, Toots Thielemans, and Larry Adler are three of the best known players of this instrument.

The 40's and 50's were the heyday of the 'Harmonica Bands' (like the "Harmonicats" and "Harmonica Rascals") and were usually led by a chromatic harmonica player.