What is the role of the guitar in a jazz band?

I play guitar in jazz ensambles and to answer your question i would have to say that how important a guitar is compared to how important a brass or sax. player is directly depends on the size of the group.

In smaller jazz combos the guitar has a lot more oppertunity for soloing, and improvisation and because there are fewer wind instruments, it is the instrument with the most presence in those cases.

In larger ensambles, however, the guitar is given a secondary role. Because the trumpet, sax, and thrombone sections are loud enough to overtake even a reasonably loud amplifier, the guitar is kind of a background instrument, heard only when the horns quiet down.

In terms of actual music, guitar players are very seldom given specific parts, and don't have to sight-read most of the music. You usually get a piece of music with just chord symbols on it and you are free to interpret them as you see fit, as opposed to playing everything 100% as it's written.

Trumpets and saxes are the classic jazz solo instruments, but even in big ensembles, I get the chance to do solos and it is very appreciated by the audiance. Justr this year I've played about 4 shows with the big ensemble, and more than 10 with the combo, and I've got to say every time the people hear a guitar break from chords and start doing a solo, they appreciate it very much, and the applause is very rewarding. Guitar solos give jazz a flavor that's not in the usual and expected brass sound.

That's really all there is to it.

The Guitar in a jazz band performs 2 roles. As part of the rhythm section it can provide a steady beat to reinforce the the bass and drums (Check out Freddie Green with Basie band in the 40's to the 60's) There are many solo jazz guitar players such as Tal Farlow (with the Red Norvo trio) who actually played "front line' melody parts and solo improvisations just as a horn player would. In some of these smaller bands without a piano the guitarist also can "comp" the "changes" in the same way that a pianist does. Almost always the electric guitar is featured in big bands and more modern groups where, as a solo instrument it can hold its own with the trumpet. However in dixieland bands guitars are rarely featured and you could say the trumpet was very important.

Hey man, in a band every instrument is important! I think a guitar forms part of the "rhythm section" of a jazz band.

Mainly to keep rhythm with some major 9's, 13's, and minor 7's, and get an occasional solo. Answering your second question I would have to say no. The trumpet is an instrument that primarily takes the lead, and isn't very good with rhythm since they really can't play chords, etc.