Came about in the 1920s as a rough fusion of Ragtime, spiritual and Marching band music.
First popular genre to based around improvisation.
Generic Jazz band consists of 'Rhythm Section' - Guitar, Drums and Piano and a varied collection of band instruments such as Sax, Clarinet, Trumpet and Trombone.
Bases of Early Jazz were Chicago and New Orleans.
Most famous early Jazz Musicians were Louis Armstrong (band leader and Trumpeter) and Duke Ellington. Whilst Armstrong's music was based on improv, Ellington's was some of the first Jazz to be notated.
Lost favour in the 1950s with the further development of Rock and Roll which took some elements of Jazz like 12 bar chord patterns and the concept of solos.
Still had some popularity in the 50s and 60s with Miles Davis and 'Kind of Blue' which is hailed as one of the best albums of all time.
Has spawned an uncountable number of subgenres such as trad jazz, cool jazz, chilled jazz, smooth jazz, acid jazz etc. etc.
Contempoary Jazz is mostly art music and is very contrived.
Erm... that's all I can remember at the moment, it's been a while. I could go get some books... but I can't be bothered