Plutarch's Lives of the Noble Greeks and Romans, commonly called Parallel Lives or Plutarch's Lives, is a series of biographies of famous men, arranged in tandem to illuminate their common moral virtues or failings, probably written at the beginning of the second century AD. The surviving Parallel Lives,comprises 23 pairs of biographies, each pair consisting of one Greek and one Roman, as well as four unpaired, single lives. It is a work of considerable importance, not only as a source of information about the individuals described, but also about the times in which they lived.

As he explains in the first paragraph of his Life of Alexander, Plutarch was not concerned with writing histories, but with exploring the influence of character, good or bad, on the lives and destinies of famous men. He wished to prove that the more remote past of Greece could show its men of action and achievement as well as the nearer, and therefore more impressive, past of Rome. His interest was primarily ethical, although the lives have significant historical value as well. The Lives was published by Plutarch late in his life after his return to Chaeronea and, if one may judge from the long lists of authorities given, it must have taken many years to compile.

The chief manuscripts of the Lives date from the 10th and 11th centuries, and the first printed edition appeared in Rome in 1470. Thomas North's 1579 English translation was an important source-material for Shakespeare. Jacob Tonson printed several editions of the Lives in English in the late 17th century, beginning with a five-volume set printed in 1688, with subsequent editions printed in 1693, 1702, 1716, and 1727.[citation needed] The most generally accepted text is that of the minor edition of Carl Sintenis in the Bibliotheca Teubneriana (five volumes, Leipzig 1852-1855; reissued without much change in 1873–1875). There are annotated editions by I. C. Held, E. H. G. Leopold, Otto Siefert and Friedrich Blass and Carl Sintenis, all in German; and by Holden, in English.

Several of the lives, such as those of Epaminondas and Scipio Africanus, are lost, and many of the remaining lives are truncated, contain obvious lacunae and/or have been tampered with by later writers.

Plutarch's Life of Alexander is one of the few surviving secondary or tertiary sources about Alexander the Great, and it includes anecdotes and descriptions of incidents that appear in no other source. Likewise, his portrait of Numa Pompilius, an early Roman king, contains unique information about the early Roman calendar.

Plutarch's Life of Romulus is a significant source of the Roman foundation myth.