A song cycle (German: Liederkreis or Liederzyklus) is a group, or cycle, of individually complete songs designed to be performed in a sequence as a unit. The songs are either for solo voice or an ensemble, or rarely a combination of solo songs mingled with choral pieces. The number of songs in a song cycle may be as brief as two songs or as long as 30 or more songs.
The term "song cycle" did not enter lexicography until 1865, in Arrey von Dommer's edition of Koch’s Musikalisches Lexikon, but works definable in retrospect as song cycles existed long before then. One of the earliest examples may be the set of seven Cantigas de amigo by the 13th-century Galician jongleur Martin Codax. A song cycle is similar to a song collection, and the two can be difficult to distinguish. Some type of coherence, however, is regarded as a necessary attribute of song cycles. It may derive from the text (a single poet; a story line; a central theme or topic such as love or nature; a unifying mood; poetic form or genre, as in a sonnet or ballad cycle) or from musical procedures (tonal schemes; recurring motifs, passages or entire songs; formal structures).
These unifying features may appear singly or in combination. Because of these many variations, the song cycle "resists definition". The nature and quality of the coherence within a song cycle must therefore be examined "in individual cases".