A free-bass system is a system of left-hand bass buttons on an accordion, arranged to give the performer greater ability to play melodies with the left-hand and form one's own chords. The left-hand buttonboard consists of single-note buttons with a range of three octaves or more, in contrast to the standard Stradella bass system, which offers a shorter range of single bass notes, plus preset major, minor, dominant seventh, and diminished chord buttons. The term "free-bass system" refers to various left-hand manual systems that provide this functionality: The Stradella system does not have buttons for different octaves of the bass notes, which limits the types of melodies and basslines that can be performed with the left hand.

Accordions are a family of box-shaped musical instruments of the bellows-driven free reed aerophone type. The essential characteristic of the accordion is to combine in one instrument a melody section, also called the diskant, usually on the right-hand keyboard, with an accompaniment or Basso continuo functionality on the left-hand. The musician normally plays the melody on buttons or keys on the right-hand side, and the accompaniment on bass or pre-set chord buttons on the left-hand side. A person who plays the accordion is called an accordionist.