Cyrill Demian (Arm. ) (17721849) was an Armenian inventor of Armenopolis origin who made his living as an organ and piano maker with his two sons, Karl and Guido, in Mariahilfer Strae No. 43 in Vienna, Austria. On May 6, 1829, Cyrill and his sons presented a new instrument to the authorities for patent - the accordion. The patent was officially granted on May 23, 1829.

Accordions (from 19th-century German Akkordeon, from Akkord—"musical chord, concord of sounds") are a family of box-shaped musical instruments of the bellows-driven free-reed aerophone type, colloquially referred to as a squeezebox. A person who plays the accordion is called an accordionist. The concertina and bandoneón are related. The harmonium and American reed organ are in the same family, but are typically larger than an accordion and sit on a surface or the floor.

The accordion is played by compressing or expanding the bellows while pressing buttons or keys, causing pallets to open, which allow air to flow across strips of brass or steel, called reeds. These vibrate to produce sound inside the body. Valves on opposing reeds of each note are used to make the instrument's reeds sound louder without air leaking from each reed block. The performer normally plays the melody on buttons or keys on the right-hand manual, and the accompaniment, consisting of bass and pre-set chord buttons, on the left-hand manual.

The accordion is widely spread across the world because of the waves of immigration from Europe to the Americas and other regions. In some countries (for example: Argentina, Brazil, Colombia, the Dominican Republic, Mexico, and Panama) it is used in popular music (for example: tango in Argentina, gaucho, forró and sertanejo in Brazil, vallenato in Colombia, merengue in the Dominican Republic, and norteño in Mexico), whereas in other regions (such as Europe, North America and other countries in South America) it tends to be more used for dance-pop and folk music and is often used in folk music in Europe, North America and South America.

In Europe and North America, some popular music acts also make use of the instrument. Additionally, the accordion is used in cajun, zydeco, jazz music and in both solo and orchestral performances of classical music. The piano accordion is the official city instrument of San Francisco, California. Many conservatories in Europe have classical accordion departments. The oldest name for this group of instruments is harmonika, from the Greek harmonikos, meaning "harmonic, musical". Today, native versions of the name accordion are more common. These names refer to the type of accordion patented by Cyrill Demian, which concerned "automatically coupled chords on the bass side".