The Soprano sax is a higher-register variety of the saxophone, a woodwind instrument invented in the 1840s. The soprano is the third-smallest member of the saxophone family, which consists (from smallest to largest) of the soprillo, sopranino, soprano, alto, tenor, baritone, bass, contrabass saxophone and tubax. 

Soprano saxs are the smallest and thus highest-pitched saxophone in common use.
The soprano has all the keys of other saxophone models (with the exception of the low A on some baritones and altos). Soprano saxs were originally keyed from low B to high E♭, but a low B♭ mechanism was patented in 1887 and by 1910 nearly all saxophones were keyed to low B♭ including sopranos. During the 1920s it became standard for sopranos to be keyed to high F. Starting in the 1950s, high F♯ was offered as an option on some sopranos, and by the 1970s most professional-level instruments had a high F♯ key. Nearly all sopranos ​made today are keyed to high F♯ as standard, and some recent professional sopranos  may have a high G key next to the F♯ key. Additionally, skilled players can make use of the altissimo register, which allows them to cover these notes and play even higher, usually regardless of their instrument's keyed range.