The contrabass clarinet is the largest member of the clarinet family that has ever been in regular production or significant use. Modern contrabass clarinets are pitched in BB, sounding two octaves lower than the common B soprano clarinet and one octave lower than the B bass clarinet. Some contrabass clarinet models have a range extending down to low (written) E, while others can play down to low D or further to low C. Some early instruments were pitched in C; Arnold Schoenberg's Fünf Orchesterstücke specifies a contrabass clarinet in A, but there is no evidence of such an instrument ever having existed. 
The contrabass clarinet is also sometimes known by the name pedal clarinet, this term referring not to any aspect of the instrument's mechanism but to an analogy between its very low tones and the pedal tones of the trombone, or the pedal department of the organ.
Subcontrabass clarinets, lower in pitch than the contrabass, have been built but only on an experimental basis.
The EE contra-alto clarinet is sometimes referred to as the "EE contrabass clarinet".
The earliest known contrabass clarinet was the contre-basse guerrière invented in 1808 by a goldsmith named Dumas of Sommières; little else is known of this instrument.
The batyphone (also spelled bathyphone, Ger. and Fr. batyphon) was a contrabass clarinet which was the outcome of W. F. Wieprecht's endeavor to obtain a contrabass for the reed instruments. The batyphone was made to a scale twice the size of the clarinet in C, the divisions of the chromatic scale being arranged according to acoustic principles. For convenience in stopping holes too far apart to be covered by the fingers, crank or swivel keys were used. The instrument was constructed of maple-wood, had a clarinet mouthpiece of suitable size connected by means of a cylindrical brass crook with the upper part of the tube and a brass bell. The pitch was two octaves below the clarinet in C, the compass being the same, and thus corresponding to the modern bass tuba. The tone was pleasant and full, but not powerful enough for the contrabass register in a military band. The batyphone had besides one serious disadvantage: it could be played with facility only in its nearly related keys, G and F major. The batyphone was invented and patented in 1839 by F.W. Wieprecht, director general of all the Prussian military bands, and E. Skorra, the court instrument manufacturer of Berlin. In practice the instrument was found to be of little use, and was superseded by the bass tuba.
Soon after Wieprecht's invention, Adolphe Sax created his clarinette-bourdon in B.
In 1889 Fontaine-Besson began producing a new pedal clarinet (see photograph). This instrument consists of a tube long, in which cylindrical and conical bores are combined. The tube is doubled up twice upon itself. There are 13 keys and 2 rings on the tube, and the fingering is the same as for the B clarinet except for the eight highest semitones. The tone is rich and full except for the lowest notes, which are unavoidably a little rough in quality, but much more sonorous than the corresponding notes on the double bassoon. The upper register resembles the chalumeau register of the B clarinet, being reedy and sweet.
None of these instruments saw widespread use, but they provided a basis for contrabass clarinets made beginning in the late 19th and early 20th centuries by several manufacturers, notably those designed by Charles Houvenaghel for Leblanc, which were more successful.
Some compositions making notable use of the contrabass clarinet include: