Antoine Joseph Adolphe Sax (November 6, 1814 – February 4, 1894) was a Belgian musical instrument designer, best known for inventing the saxophone.

Adolphe Sax was born in Dinant in Belgium. His father, Charles Joseph Sax, was himself an instrument designer, who made several changes to the design of the French horn. Adolphe began to make his own instruments at an early age, entering two of his flutes and a clarinet into a competition at the age of fifteen. He subsequently studied those two instruments at the Royal School of Singing in Brussels.

Having left the school, Sax began to experiment with new instrument designs, while his father continued to produce conventional instruments to bring money into the household. Adolphe's first important invention was an improvement of the bass clarinet design which he patented at the age of 20.

In 1841, Sax relocated permanently to Paris and began work on a new set of instruments which were exhibited there in 1844. They were keyed bugles, and although he had not invented the instrument itself, his examples were so superior to those of his rivals that they became known as saxhorns. They are today widely used in military bands and sometimes in orchestras. The saxhorn also laid the groundwork of the modern euphonium.

Sax was also busy around this time inventing the instrument for which he is now best known, the saxophone. The composer Hector Berlioz wrote approvingly of the new instrument in 1842, but the instrument was not patented until 1846, after he had designed and exhibited a full range of saxophones (from soprano to bass). These instruments made his reputation, and secured him a job teaching at the Paris Conservatoire.

Sax continued to make instruments later in life, as well as presiding over a new saxophone class at the Paris Conservatoire.

He died in 1894 in Paris and was interred in the Cimetière de Montmartre.