More than any other instrument, the guitar is a world unto itself. Whereas a jazz saxophonist or trumpeter is likely to think of himself as a jazz musician first, a jazz guitar player will think of himself first and foremost as a guitarist. Judging by a new four-CD box set, “Progressions: 100 Years of Jazz Guitar” (Columbia/Legacy 86462), both players and fans of the guitar are less interested in playing by the rules of jazz than in exploring what the instrument can do.

The set shows how jazz guitar has, for most of its 100-year history, existed primarily by interacting with other kinds of music: blues, country music, Hawaiian music, Brazilian music, rock ‘n’ roll, and mass-market pop. In other words, the musical genre known as “jazz guitar” has a thin and narrow mainstream, and the producers of “Progressions” are more interested in the wide-reaching fringes – how else can you explain the inclusion of Jimi Hendrix and the exclusion of Bucky Pizzarelli? The result is a fascinating set that contains some great music but does little to clarify what exactly the concept of “jazz guitar” might mean.

The box’s best moments are in the first disc and a half, which covers the 78 era. Any discussion of jazz guitar must begin with the three short-lived pioneers of the pre-bop era – Eddie Lang, Django Reinhardt, and Charlie Christian – and here the box’s producers make the right choices. Lang is represented by “Add a Little Wiggle,” on which we hear, for the first time, a guitarist soloing with all the harmonic ingenuity, sensitivity, and swing of a horn player. Reinhardt, as we hear on “Honeysuckle Rose,” brought an Art Tatum influenced harmonic sensibility, enhanced compositional skills, and a gypsy soul to jazz. Christian, captured here on “Solo Flight,” his classic feature with the Benny Goodman Orchestra, simultaneously electrified jazz and pointed the way to the modern era in the course of an especially brief career.

The box also includes lesser-known but outstanding figures like Carl Kress, Oscar Aleman, and the recently deceased Al Casey. Further, I am gratified the producers included Freddie Greene and Eddie Condon, outstanding rhythm guitarists who recorded prolifically but left few solos on record. And the inclusion of names new to me – Casey Bill Weldon, Sam Moore, Eddie Bush – indicates that the producers are also concerned with reclaiming neglected and lost figures. Another rarity is the set’s first track, a 1906 banjo recording of “St. Louis Tickle” that touches on elements of jazz, ragtime, vaudeville, and pop. (The tune was alleged by Jelly Roll Morton to be based on a blues written by the quasi-mythical first jazzman, Buddy Bolden.)

Elsewhere, though, the producers have made some unfortunate decisions to deviate from the jazz mainstream and into the pop arena. The marvelous stylist Oscar Moore, for example, is not represented by one of the many pure jazz instrumentals he cut during his 10-year collaboration with Nat King Cole, but by “Gee Baby, Ain’t I Good to You,” which has heavy elements of pop and blues. Even more glaring is the inclusion of “Runnin’ Wild,” a track by Les Paul and Mary Ford. Mr. Paul is a one-man justification of the set’s premise – he has been a major figure in jazz, pop, and country – but there are plenty of recorded examples of him playing pure jazz (the most famous one, coincidentally, was in the company of Nat King Cole). I can think of no justification for giving us one of the ghastly chart hits by the Paul-Ford combination.

The issue of jazz values competing with guitar values becomes most problematic when the set reaches the 1970s. In the decade after John Coltrane and before Wynton Marsalis, the guitar was briefly the most popular instrument in jazz, and seemingly most of the musicians who picked up the guitar in that decade were determined to find a halfway point between jazz and rock.

I will concede that fusion, as it was called, was an important movement, but it is entirely over-represented here: There is track after track by ’70s guitar gods, much of it containing only marginal jazz content. The fusion confusion is further illustrated by the inclusion of Latin-rock giant Carlos Santana and smooth-jazz player Earl Klugh. On the plus side, there are some fascinating samples of postmodern experimentalists such as British avant-gardist Derek Bailey, soundscaper Bill Frisell, and outerspace bluesmen Sonny Sharrock and James Blood Ulmer.

To my dismay, though, the box neglects the contemporary heirs to Lang, Reinhardt, and Christian. Where are Joe Cohn, Howard Alden, Russell Malone, Mark Whitfield, James Chirillo, Gene Bertoncini, Frank Vignola, and John Pizzarelli? I can only imagine that they are barred because they stay firmly in the jazz tradition, and have no apparent interest in fusing jazz with something else. The point being made by “Progressions” is clear: As far as the jazz guitar is concerned, the fringes and the margins are more important than the mainstream.

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The sixth annual Djangofest kicks off tonight at Birdland, and fans of jazz guitar can look forward to five days of ultra-competitive jam sessions in which heavy-hitting nouveau Gypsy musicians try to out-Django each other. The daily lineup includes guitar stars Angelo Debarre and Dorado and Samson Schmitt, along with a supporting cast of Ludovic Beier, Pierre Blanchard, and Tchavolo Hassan. But the guest stars will probably determine what night you choose to head out to Birdland: They include Ken Peplowski (tonight), Harry Allen (tomorrow), Lew Tabackin (Thursday), Roger Kellaway (Friday), Joel Frahm (Saturday), and Dominick Farinacci (Sunday). While I would still love to see producers Ettore Strata and Pat Phillips tackle a more ambitious program of Reinhardt compositions – possibly with a full orchestra – their Djangofests are always exciting.

wfriedwald@nysun.com