There are several types of concertinas and related "squeezeboxes". The English Concertina was invented in the mid-1800's by an English physicist, Sir Charles Wheatstone (who is also famous for discovering the "Wheatstone Bridge" in electrical physics).
The concertina is in a family of "free reed" instruments, which includes the accordion, melodion, harmonium and even the harmonica. These instruments have flat metal reeds which vibrate as the air passes over them, with each musical note being determined by the length of the reed.
The concertina pictured here is a 48-key treble. It's an English concertina, which means that any given button will produce the same note whether the bellows are pressed or pulled. An "Anglo" concertina has a similar shape, but is set up with a different button pattern, with each button producing a different note on the push and pull of of the bellows.
Concertinas tend to be difficult to find, and can be very expensive due to their complex design. Timmy's concertina was made by Steve Dickinson in England. Dickinson has retained the Wheatstone brand name and he crafts beautiful instruments using some of the original tools and jigs from the old Wheatstone factory. His instruments are copies of the finest Wheatsone models from the early 20th century.
If you are interested in finding a concertina for sale, try The Button Box in Amherst, MA at www.buttonbox.com.