A concertina is a free-reed musical instrument, like the various accordions and the harmonica. It has a bellows and buttons typically on both ends of it. When pressed, the buttons travel in the same direction as the bellows, unlike accordion buttons which travel perpendicularly to it. Also, each button produces one note, while accordions typically can produce chords with a single button.
The concertina was developed in England and Germany, most likely independently. The English version was invented in 1829 by Sir Charles Wheatstone and a patent for an improved version was filed by him in 1844. The German version was announced in 1834 by Carl Friedrich Uhlig.
The folk revival movements of the 1960s led to a modest resurgence in the popularity of the concertina particularly the Anglo. More recently the popularity of the concertina again seems to be experiencing a resurgence, particularly the Anglo in the traditional music of Ireland. Renewed interest in tango since the 1980s has also seen interest in the "Bandoneón" increase.