Abraham Zevi Idelsohn (Hebrew: אַבְרָהָם צְבִי אידלסון Avrohom Tzvi Idelsohn in Ashkenazi Hebrew; middle name also rendered Tzvi, Zvi, Zwi, or Zebi; July 14, 1882 – August 14, 1938) was a prominent Jewishethnologist, musicologist and composer, who conducted several comprehensive studies of Jewish music around the world.
Idelsohn is generally acknowledged as the “father” of modern musicology. During his time in Jerusalem, he noted a great diversity of musical traditions among the Jews living in the region. Idelsohn examined these traditional melodies and found recurring motifs and progressions that were not found in any other national music. This suggested a common origin for musical phrases that went back to Israel/Palestine in the first century C.E. He found that these motifs fell into three distinct tonal centers, which corresponded to the Dorian, Phrygian, and Lydian modes of the ancient Greeks. Each of these modes elicited a distinct psycho-emotional response. The Dorian Mode was used for texts of an elevated and inspired nature; the Phrygian for sentimental texts, with their very human outbreaks of feeling, both of joy and grief; and the Lydian was used in composing music for the texts of lamenting and confessions of sins. Idelsohn further categorized and defined these motives as ones that either prepared a musical phrase, began it, or concluded it. 
His works include the monumental Thesaurus of Hebrew Oriental Melodies (10 volumes, 1914–1932) and Jewish Music (1929). He is considered to be the author of the lyrics of the famous Jewish folk song "Hava Nagila."