What constitutes kugak (Korean traditional music), and what differentiates it from today’s dominant South Korean music culture, that is, Western-originating genres of ŭmak/sŏyang ŭmak? When the National Gugak Center (Kungnip kugagwŏn, initially known as the National Classical Music Institute) resumed operations following the Korean War, its repertoire centred on court and literati traditions (chŏngak). However, in 1953, seeking to enhance performances, it recruited Kim Yundŏk (1918–1978), a musician expert in sanjo (“scattered melodies” for solo melodic instrument and drum). The soundtrack to the 1955 film, Yangsando, created by the Center scholar musician Sŏng Kyŏngnin (1911–2008), therefore featured court and literati repertoire but also Kim, together with a further popular “folk” musician, the p’ansori (epic storytelling through song) expert Pak Ch’owŏl (1917–1983). The concept of kugak continued to broaden as – in Korean terms – formation (hyŏnsŏng) over time was replaced by composition (chakkok), as new kugak pieces were commissioned, particularly following the 1959 establishment of Seoul National University’s kugak degree. By the beginning of the new millennium, fusions of kugak instruments and Western instruments – and of kugak with jazz and pop – were embraced, particularly as Gugak FM, a radio station devoted to kugak, began operations. Further diversity came as kugak musicians worked collaboratively with musicians and composers abroad. And, since 2015, eight MA dissertations and two PhD dissertations have been successfully defended within Seoul National’s kugak department that concern only works by non-Korean composers. This paper charts the debates and arguments about kugak, its idioms and its identity. Similar issues are, of course, pertinent across East Asia, but this paper asks whether, as the boundaries between kugak and other musics blur, as kugak musicians operate in global and glocal contexts, and as the tautological perception of non-Korean actors creating kugak recedes, a distinct kugak sphere can be sustained.