Hellenica is one of the most important primary sources for the History of the Peloponnesian War and the war's aftermath. Many consider this a very personal work, written by Xenophon in retirement on his Spartan estate, intended primarily for circulation among his friends, for people who knew the main protagonists and events, often because they had participated in them. It covers the events in Greece from 411 to 362 BC, and is considered to be the continuation of the History of the Peloponnesian War by Thucydides.

Xenophon of Athens (c. 431 BC – 354 BC) was an ancient Greek philosopher, historian, soldier, mercenary, and student of Socrates. Xenophon's works span several genres and are written in plain-language Attic Greek, for which reason they serve as translation exercises for contemporary students of the Ancient Greek language. As a historian, Xenophon is known for recording the history of his time, the late-5th and early-4th centuries BC, in such works as the Hellenica, which covered the final seven years and the aftermath of the Peloponnesian War (431–404 BC), thus representing a thematic continuation of Thucydides' History of the Peloponnesian War.