Nostalgia is a sentimentality for the past, typically for a period or place with happy personal associations. The word nostalgia is a learned formation of a Greek compound, consisting of νόστος (nóstos), meaning "homecoming", a Homeric word, and ἄλγος (álgos), meaning "sorrow" or "despair", and was coined by a 17th-century medical student to describe the anxieties displayed by Swiss mercenaries fighting away from home. Described as a medical condition—a form of melancholy—in the early modern period, it became an important trope in Romanticism.

Nostos is a theme used in Ancient Greek literature, which includes an epic hero returning home, often by sea. In Ancient Greek society, it was deemed a high level of heroism or greatness for those who managed to return. This journey is usually very extensive and includes being shipwrecked in an unknown location and going through certain trials that test the hero. The return is not only about returning home physically, but also focuses on the hero retaining or elevating their identity and status upon arrival. The theme of nostos is brought to life in Homer's The Odyssey, where the main hero Odysseus tries to return home after battling in the Trojan War. Odysseus is challenged by many temptations, such as the Sirens and the Lotus-eaters. If Odysseus had given into these temptations it would have meant certain death and thus failing to return home. Nostos is used today in many forms of literature and movies.