Sébastien Érard is a French piano and harp maker whose improvements in both instruments were largely responsible for their modern forms. The son of a cabinetmaker, Érard was apprenticed to a harpsichord builder in Paris; there, about 1775, he invented a mechanical harpsichord and earned the patronage of the Duchess of Villeroi. At a workshop on her estate, he made the first French square piano (1777). Thereafter, with his brother Jean-Baptiste, he opened his first shop, and success led to the opening of a London branch in 1786.

Eventually the business passed to Sébastien’s nephew Pierre, who continued to enhance the firm’s reputation with mechanical innovations. Among the firm’s inventions were a novel grand piano action (key mechanism) that allowed quicker repetition of notes (1809), a double-action pedal harp that allowed greater ease of changing key while playing (1801–10), and new methods of constructing harp and piano frames. The firm had produced about 100,000 instruments by the end of the 19th century and pioneered in building harpsichords in the early 20th century.