This article gives you a short overview over what a clarinet is. You find more details in the articles of this site, the link page, plus lots of helpful links in Wikipedia.
The Clarinet Is...
The clarinet is one of the younger woodwind instruments with a single reed and cylindrical bore. When you talk about "the" clarinet in general you usually refer to the A- or B flat (soprano) clarinet, although there is a whole clarinet family ranging from the small and high E flat to the very big and ultradeep sounding contrabass clarinet, which is about 2,70 meter (appr. 8.86 feet) long.
Looks
The B flat clarinet, which is by far the most common, is about twice as big as a recorder. It consists of several parts, usually made of black grenadilla wood and silver-plated keys. There are, too, clarinets made of synthetics / plastic, Plexiglass or metal. From a distance the instrument may look similar to an oboe. In contrast to the oboe's thin double reed, looking like a straw, the clarinet has got a wide mouth piece with a single reed fixed onto it. Furthermore it has got a cylindrical bore, that is, the full length is of the same diameter (except for the very lower end called the bell), much in contrast to most other wind instruments.
Tone Range and Sound
The clarinet's tone range is wider than that of all other wind instruments. All instruments play the E (E3 - some go lower) and most players can reach a high c7, that means nearly 4 octaves. The dynamic (loudness) ranges from practically unhearable ppp (no other wind instrument can play quieter) to a hurting fff (only brass and saxophones can play louder).
Both in sound and playing techniques the clarinet is one of the most flexible instruments at all. You will find that it shows a very different sound in the different registers - more characteristic than any other wind instrument. You can play virtually all forms of articulation with a clarinet - extremely short staccato, a perfect legato (binding of notes), vibrato when it is needed, even a glissando (that is changing the pitch from one tone to another without having to interrupt).
A Short History
The clarinet's history begins with its invention around 1700: The German instrument maker J.C. Denner developed it based on a very simple shepherd's instrument, the chalumeau, which then had a range of about one octave. Until today several clarinet systems have been developed, the most widely used being the French Boehm system (used in English speaking countries, too) and the German system (in German speaking countries). Since 1800 (Mozart, Weber, Beethoven) the clarinet is fully established in symphonic music, popular music, dance- and military music and then later on in Jazz and pop, but is also used in Indian, Persian and Turkish music, Gipsy, Kletzmer and even Arabian music with its non-European scales.
National Styles
There is a diversity of national styles and quite different ideas of how a clarinet should sound, with the German and French schools being the most prominent (the English and North American in between, but leaning more towards the French). At least in the question which instrument type to use the French school is clearly dominating the world (except for Germany and Austria, where they use their own instrument types).
What To Play
In the classical symphony orchestra there are at least two to three clarinettists playing the B flat or A clarinet, in addition there often is an E flat clarinet player and a bass clarinet player when needed. The clarinet held its role in popular music until the saxophone took over in the mid 20th century, when electronic amplifiers (microphones and e-guitars) made a far louder tone necessary.
In the symphonic wind band and the marching band the clarinets are used to replace the strings like violins and violas - as a result there are many more clarinet players (typically about 20) in this type of orchestra. In dance orchestras and jazz big bands the clarinet is often played by the same musicians who play the saxophone, too, because of the same mouthpiece and the similar technique.
An Instrument For You?
Clarinets are not extremely expensive - you get "quite good" new instruments as well as a better but used ones starting from about 500 Euros (a little more than 500 US$). Neither is the clarinet large or difficult to carry about. The instrument case fits into an ordinary rucksack - just discuss logistics with a bassoonist, a tuba-player or a drummer! A young child can start to learn playing the clarinet as soon as it has his/her adult teeth are there and the hands are big enough. Depending on your ambition and time invested in exercising (like an hour per day) you can learn enough in two years to be able to play in a beginners' orchestra or band (this still leaves you some way to go to become a world class solo clarinet player, off course).
German Version