Posillipo (Italian: [poˈzillipo]; Neapolitan: Pusilleco [puˈsilləkə]) is an affluent residential quarter of Naples, southern Italy, located along the northern coast of the Gulf of Naples.

From the 1st century BC the Bay of Naples witnessed the rise of villas constructed by elite Romans along the most panoramic points of the coast, who had chosen the area as a favourite vacation spot. The remains of some of these, around the imperial pleasure villa of the Roman emperors, as well as the Tunnel of Sejanus can be seen today in the Parco archeologico del Pausilypon, or Pausilypon Archaeological Park, and elsewhere.

Posillipo is a rocky peninsula about 6 km long surrounded by cliffs with a few small coves with breakwaters at the western end of the Bay of Naples. These small harbours are the nuclei for separate, named communities such as Gaiola Island and Marechiaro.

Posillipo is mentioned in ancient Greek and Roman sources. As part of Magna Graecia, the Ancient Greeks first named it Pausílypon, meaning "respite from worry". The French Homeric scholar Victor Bérard identified Posillipo as the land of Homer's Cyclopes. From the 1st century BC the beautiful coastline of Campania attracted wealthy Romans as a place to build elaborate and grand villas as retreats.

Of ancient Pausilypon the most visible ruins are those of the notorious villa of Vedius Pollio, later to become an imperial villa. The villa was described by the poet Ovid as "like a city". Most notoriously, he kept a pool of lampreys into which slaves who incurred his displeasure would be thrown as food, a particularly unpleasant means of death, since the lamprey "clamps its mouth on the victim and bores a dentated tongue into the flesh to ingest blood". However, the emperor, Augustus, on visiting Pollio and witnessing the condemnation of a slave, took action against Pollio and saved the slave, an incident widely documented in writings of the era (see Vedius Pollio for more details).

Vedius died in 15 BC and was probably forced to bequeath a large part of his estates, including the villa, to the emperor Augustus. Although Augustus had Vedius' mansion in Rome razed, Pausilypon was rebuilt and extended to become a palace, which remained in imperial possession at least until the time of Hadrian.

In the 17th century the property of the site of the imperial villa passed to the family Maza who, for several generations, showed an interest in archaeology and Francesco Maria Maza (c. 1680) was the author of inscriptions which he affixed to the so-called 'Piscine of V.Pollio' and to the 'Temple of Fortune' which were in situ as late as 1913. However the Maza collection was dispersed and the loss to archaeological science was irreparable as a catalogue had never been prepared. Several objects of art from Posillipan sites found their way into the hands of Spanish collectors, and are still no doubt among the Roman antiquities in Spain. Many fine pieces were taken to Mergellina and lost among the other ornaments of the villa of the Duke of Medina.

In 1820 the southern portion of the property was purchased by a well-known Neapolitan archaeologist, cavaliere Guglielmo Bechi, and his name was associated with the Villa for more than half a century. He did much excavation, but again without publication of results.