Xenophon accompanied a large army of Greek mercenaries hired by Cyrus the Younger, who intended to seize the throne of Persia from his brother, Artaxerxes II. Though Cyrus' army was victorious in a battle in Babylon, Cyrus himself was killed in battle and the expedition rendered moot. Stranded deep in enemy territory, most of the Greek generals were subsequently killed or captured by treachery. Xenophon played an instrumental role in encouraging the Greek army of 10,000 to march north to the Black Sea. This is the story he relates in this book.
The Greek term anabasis referred to an expedition from a coastline into the interior of a country. The term katabasis referred to a trip from the interior to the coast. Since most of Xenophon's narrative is taken up with the march from the interior of Babylon to the Black Sea, the title is something of a misnomer.
Socrates makes a cameo appearance when Xenophon asks whether he ought to accompany the expedition. The short episode demonstrates the reverence of Socrates for the oracle of Delphi.
Historically the Anabasis has been one of the first unabridged texts presented to students of the classical Greek language due to its clear and unadorned style, much like Caesar's Gallic Wars for Latin students.
One of the best and most easily found translations is Rex Warner's The Persian Expedition.