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There are different styles to jazz. It is a music that has evolved with time. Recognizing the styles won't make you enjoy the songs any more, but it may help you for instance, if somebody tells you, "this is a great bebop CD," you will have an idea what it is, and you can recognize which styles you have a preference for. I don't think there is a person alive who likes ALL jazz. A lot? Yes. All? No. There is surely some guy out there who grates your nerves. :)
With that in mind, here are some of the different styles...not all the styles (because I don't know them all), but some of them:
Dixieland -- This is the style that is most closely related to New Orleans and especially the marching funerals from the area. It is a very happy music. The instrumentation consists of a trumpet, that plays the main melody -- usually with a lot of bounce and flair, the trombone, which plays a counter-melody; the clarinet dances around the melody (kind of like a yapping Chihuahua nipping at your ankles :); the piano played the chords, the tuba was frequently used in place of a bass, and it kept the rhythm, along with the drums. It is a 2/4 rhythm (or "Ooom pah, Ooom pah", if 2/4 means nothing to you). Sometimes, the early Dixieland groups recorded with a banjo keeping rhythm, since they didn't have microphones (they used something resembling a megaphone) and the drums were too overpowering. Examples of this style are the Original Dixieland Jazz Band and Wild Bill Davidson and the Commodores.
Hot Jazz -- This is a music style I am not very familiar with. I would like to learn more about it, but my money is spent elsewhere, jazz-wise. This music is from the "Jazz Age" in history (also known as the "Roaring 20s"). It is the link between Dixieland and Big Band Swing. The combos got bigger and started using, for instance, 2 trumpet players. It's not as polished as Swing music. The music really cooks from this era, though--don't get me wrong. Examples of this music are Jelly Roll Morton's Red Hot Peppers and Louis Armstrong's Hot Fives (and Hot Sevens) as well as Fletcher Henderson's orchestra.
Swing (or Big Band) -- This is jazz that is more formal and usually less improvised. The structure is very tight. The instrumentations often consists of "sections", such as 4 trumpets, 4 trombones, and 4 "reeds" (Saxophones of various types and/or clarinet.) as well as drums, guitar, piano, and bass. They used techniques such as "call and response", where a section would play a riff and another section would repeat it. The music uses a lot of riffs, or a musical phrase played over and over (check out Glen Miller's "In the Mood" for an example of this). This music was very popular and very danceable. It nearly died in the late 1950s and all but disappeared in the 1960s and 1970s, due to decreasing popularity and high expenses (a lot of members to pay), but it is making a comeback. Examples of this music are the big bands of Benny Goodman, Count Basie, Tommy Dorsey, and Duke Ellington.
Bebop -- During the early 1940s, some very talented musicians grew tired of playing the same music in their jobs with swing bands. After the band played, they would stick around for jam sessions. A group of enormously talented musicians: Charlie Parker, Thelonious Monk, Dizzy Gillespie, Kenny Clarke, and Charlie Christian invented a style that became known as bebop. It was less structured than say, swing, but depended heavily on improvisation and because these guys were leading the way, it required virtuosity, as well. The improvised solos, rather than being based on ornamenting the melody, was based on complex chords that changed rapidly. The music is very driving and you can usually recognize it, because a) You probably cannot whistle the melody after hearing it, and b) the drums drive hard, especially when keeping time on the cymbals! Examples of this music, other than those listed above, would also include Dexter Gordon, Fats Navarro, and Bud Powell.
Cool (or West Coast jazz) --This music came to be as a result of the Miles Davis' nonet and a series of recordings that later became known as The Birth of the Cool (Click link to view album). The style uses the chord changes, like bebop, but lacks the intensity and the "piss and vinegar" of bebop. The music is more laid back. Many say it lacks the "emotional intensity" of bebop. The drummers in cool music often use brushes, and hence, you do not get that driving rhythm from the drums. This music was very popular in the early to mid 1950s and some examples of players from this genre include Stan Getz, Gerry Mulligan, Paul Desmond, and Chet Baker.
Hard Bop -- This music was a outgrowth from bebop. It also uses complex chord changes. However, hard bop mixes bebop with gospel and blues, providing a more "emotional" music. Sometimes, the line between the music styles gets blurred (and you will see me refer to both as "bop"). This music was also known as "East Coast jazz" during the 1950s. Examples of this genre include: Art Blakey, Horace Silver, Lee Morgan, and Cannonball Adderly.
Third Stream -- This was an attempt by George Russell to fuse classical music with jazz during the mid-1950s. Improvisational music with structured, composer-oriented music. Go figure. I hear his 3 movement piece "All about Rosie" is very good, though. I don't have any music from this genre.
Progressive Swing -- An attempt in the 1950s to fuse
Swing (Big Band) music with elements of bebop. An example of this is Stan Kenton's
Big Band. I don't have any of this music.
Modal -- This music was an extension of theories that George Russell presented in his book The Lydian Chromatic Concept of Tonal Organization for Improvisation. (Sounds more like a thesis!) In the late 1950s, bop was starting to run its course. The chord changes were becoming more rapid and constrictive, since soloist had to play follow the chords,) and also because after playing their 32 measures (click here for a more detailed explanation), the soloist had to play the same chord changes again. .Also, the style was about 15 years old, so the novelty and to some extent, the creativity, was disappearing. What modal improvisation did was use slower moving chord changes, and freed up the soloist to improvise more based on scales, rather than the rapidly changing chords of bebop. The result more melodic solos. Miles Davis' groups of the late 1950s popularized this music and John Coltrane spent the early 1960s taking this form of jazz to new heights. Bill Evans and McCoy Tyner are two more examples of fine modal players.
Free jazz (a.k.a. "The New Thing"). Free jazz took the concepts of modal one step farther: It based it's solos on no structure (hence, it "freed" up the soloist to play anything). The solo became the melody and the players played off of musical ideas that each other were playing. This sometimes comes off as sounding dissonant, especially when multiple people play their own thing simultaneously. A little bit of it usually goes a long ways with me, so I don't listen to much. The music had something of an "angry" edge to it, and was a musical reflection of the turbulent 1960s. Although he mastered hard bop and modal jazz, John Coltrane played this music during the last years of his life and became the musical figurehead who lent credibility to it (and the music's popularity basically died with him). The father of this genre is Ornette Coleman. Cecil Taylor is another example of an important figure from this style.
Bossa Nova -- Stan Getz popularized this music, and it became an outgrowth of Cool jazz. It uses Latin Bossa Nova music mixed with jazz improvisation. If you have heard the song "The Girl from Impanema," you have heard Bossa Nova (and Getz plays the saxophone solo). Getz was not supportive of Free Jazz and decided to go in this direction. It was popular in the 1960s (and some say it saved jazz during this period), but became something of a fad.
Fusion -- Miles Davis created this music form of jazz with his record Bitches Brew. The music blends jazz with rock music. It was enormously popular in the 1970s. During the 1960s, a lot of younger people were no longer interested in jazz and looked upon it as something you keep under glass in a museum. This was the time of rebellion and "trust no one over 30", so unfortunately, jazz became of casualty of this type of thinking. Miles decided to "take the music to the audience" and this was the result. The music used traditional jazz instruments, such as the trumpet, drums, and saxophone, but it added electrical versions of other instruments, such as keyboards, guitar, and bass (and Miles, for instance, used a "wah wah" pedal with his trumpet during this period). Blood, Sweat, and Tears was a popular band from this genre (you have probably heard "Spinning Wheels"). Many of Miles' sidemen went on to become some of the bigger names in this genre, such as Chick Corea's group Return to Forever; John McGlaughlin's group The Mahavishnu Orchestra; or Tony Williams' Lifetime; and Joe Zawinul and Wayne Shorter's group Weather Report.
Neo-Classical -- At the end of the 1970s/early 1980s, jazz had become so fused with Rock and other forms of music that it was beginning to become hard to tell where jazz began and ended. Many people were proclaiming that "Jazz is dead." Some of the younger players didn't care for the directions jazz took with Free Jazz and Fusion in the 1960s and 1970s and decided to look backwards for inspiration. The result is bop-based music (and some other forms, such as Dixieland) with some modern touches. The biggest name from this genre is Wynton Marsalis. Other "young lions" (as they have become known as) include: Joshua Redman, Roy Hargrove, and Branford Marsalis.