Polyphony in the Caucasus Republic of Georgia is an extremely ancient art; Herodotus wrote of Georgians going into battle singing. Manuscripts of Georgian chants written in neums (now indecipherable) date back to the 9th century C.E., written down by monks and other members of the clergy. It is, however, primarily an oral tradition, and as such is nearly impossible to date; certainly it has been an integral part of Georgian culture for milleniae. Georgians often stress the age of their polyphonic tradition, in conversation with Western musicians and musicologists, as a matter of national identity and pride. Oral transmission continues to the present day, in some cases much as it has for centuries: songs are learned by each new generation from the previous one, sometimes passed down linearly in families or villages, with close attention paid to the teacher's manner of singing the intonation and unique regional styles of ornamentation.. However, a large body of notated Georgian folksong does exist, much of which dates from the work of Soviet ethnomusicologists. Dimitri Araqishvili and others notated songs before the Bolshevik Revolution, and even German scholars Robert Lach and Siegfried Nadel transcribed Georgian folk songs as sung by Georgian POWs in Germany during WWI.
Georgian music has a very distinctive sound to Western ears, not often consonant and not always pleasing. Songs consist of (for the most part) two or three parts, sometimes four. Many songs, particularly those developed for wedding, work and dance, are antiphonal. Each vocal line in a Georgian song is independent and contrary motion is omnipresent. The harmony is close, often triadic, though a high yodel or krimanchuli which leaps fifths is sometimes added in on top. The contrary motion of the vocal lines, especially between the first and second, results in a plethora of major seconds which strengthen the texture. Very peculiar indeed to ears trained on Western art music is the Georgian "neutral third", where the third of a triad falls between the major and the minor sonorities, and is often shifted closer to one or the other depending on the direction of the harmony or vocal line. The fifth is the main unit, rather than the octave, and harmonies and voice leading are shaped accordingly. Singers are expected to improvise in most regional secular styles, though it is rare to hear a sacred chant altered in performance.
Georgian regional styles are marked and, once the listener is familiar with them, many are easily identifiable. Guria has highly complex and freely individual vocal lines for each three-part song, often with large sections improvised to strings of nonsense syllables such as abadelia, wodelia and naninewoda, and sometimes including the krimanchuli above the usual three-voice texture. Kakhetian table songs feature a bass line or bani that is a drone, in which anyone present can take part, with two voices (soloists) moving in melismatic and beautifully ornamented lyric lines above it, both independently and together. Svan songs are generally rhythmically homophonic (insofar as the rhythm of the words are concerned, at least) and glory especially in the "crunchy" sounds of major seconds and higher fourths where Western ears might expect thirds. These are only a few examples; Georgia has nineteen official provinces, and eight major regions. Singers, especially older singers, of traditional music from one region may not be familiar with the songs and styles of other regions, though today the dissemination of both traditional and tradition-influenced pop music on the radio and on tv is such that most households have at least a nodding acquaintance with other areas.
For this brief digest, I am indebted to the many writings of Carl Linich of Trio Kavkasia, who has produced several descriptions of Georgian folk polyphony both for his trio's publications and for those of the Tbilisi State Conservatory's released material.