Alexandrine is a name used for several distinct types of verse line with related metrical structures, most of which are ultimately derived from the classical French alexandrine. The line's name derives from its use in the Medieval French Roman d'Alexandre of 1170, although it had already been used several decades earlier in Le Pèlerinage de Charlemagne. The foundation of most alexandrines consists of two hemistichs (half-lines) of six syllables each, separated by a caesura (a metrical pause or word break, which may or may not be realized as a stronger syntactic break):

o o o o o o | o o o o o o

o=any syllable; |=caesura

However, no tradition remains this simple. Each applies additional constraints (such as obligatory stress or nonstress on certain syllables) and options (such as a permitted or required additional syllable at the end of one or both hemistichs). Thus a line that is metrical in one tradition may be unmetrical in another.

Where the alexandrine has been adopted, it has frequently served as the heroic verse form of that language or culture, English being a notable exception.