Accordions and concertinas are portable keyboard instruments. Both accordions and concertinas are played by compressing or expanding bellows while pressing buttons or keys. Accordions play the melody on the right side, while the left side provides rhythmic and harmonic accompaniment. Concertinas play melody on both left and right sides. Accordions typically can produce chords with a single button. Concertinas have no chords; each button produces one note. On accordions proper, the button or key travel is perpendicular to the bellows, while concertinas have buttons that travel in parallel to the bellows. Accordions and concertinas are most often featured in traditional or folk music. There are many styles of music that favour one type of "squeezebox" or another.