Lục bát (Vietnamese: [lùkp ɓáːt], Hán tự: 六八) is a traditional Vietnamese verse form - historically first recorded in chữ nôm script - that is deeply tied to the soul of Vietnamese culture and people. "Lục bát" is Sino-Vietnamese for "six eight", referring to the alternating lines of six and eight syllables. It will always begin with a six-syllable line and end with an eight-syllable one. A related measure is the Song thất lục bát.
Unlike other verse forms which are traditionally enjoyed only by high-class Vietnamese, lục bát is traditionally composed and enjoyed by people of all classes, from the lowly peasants to the noble princes. It can be regarded as a living style of Vietnamese people. The rich treasure of Vietnamese folk poems (ca dao), which consists of hundred thousands of verses that reflect on life, morality, human relationship, and nature beauty, are almost entirely composed in lục bát form. The 3774 verses in "Quốc Sử Diễn Ca" (Epic Song of National History) composed by Vietnamese poet Lê Ngô Cát under the reign of King Tự Đức are also entirely in the form of lục bát. Poet Nguyễn Du of the Lê dynasty also composed 3254 lục bát verses, telling the story of an unfortunate beauty in his renowned epic Truyện Kiều (The Tale of Kiều).
Tones are among the most important elements in Lục Bát as well as the other Vietnamese verse forms.
In poetry, the six tones of Vietnamese language are divided based on their falling and rising nature into two categories: bằng (flat) and trắc (sharp or non-flat).
There is more than one way to categorize Vietnamese tones and this categorization is only used in poetry. Also, though tone huyền is classified in the bằng category, it is actually a low falling tone.