The Yapese Empire was an ancient maritime empire located in the western Caroline Islands in the north Pacific region of Micronesia since around the 9th century, AD. In circa 950 AD, Yap became the seat of the empire when Gatcheper village in the chiefdom of Gagil (modern-day Gagil Municipality) established an expansive maritime trade network and exerted socioeconomic and political influence to its neighboring islands to the east. Although small and informal compared to other marine empires, the empire at its peak covered over 1,300 kilometers, stretching from the Yap main islands to parts of modern-day Chuuk State. The empire coexisted with the Tongan Empire located in the southern Pacific.

The empire covered over 1,300 kilometers of the north-western Pacific and included a vast number of island groups and low-lying coral atolls. The territory consists of both ruling and constituent islands, and they are indicated below. The Yapese Empire consists of islands stretching from Yap main island in modern-day Yap State to some atolls in the western part of Chuuk State.

A variety of languages were spoken in the empire. Yapese was spoken on the main islands while Ulithian, Woleaian, Satawalese, Nguluwan, and Puluwat languages were spoken on the constituent islands and atoll groups.

The Woleaian script, also sometimes known as the Caroline Islands script, was the only indigenous writing system developed in the region. It was a syllabary used in Woleai until the mid-20th century. Some of the characters were based on Latin letters whereas the origins of other characters are not known. It was used by an estimated 1,600 people.

Before the arrival of Western colonial powers in the Micronesian region, Yap and all of its constituent islands and atolls practiced traditional animistic religions with different sets of mythologies, customs, practices, and rituals. Yapese mythology bears some resemblance to Chuukic mythology although the direction of diffusion is unknown.

The empire had a form of tribute system known as sawey. According to the sawey system, the empire demanded regular tributes known as pitigil tamol to be presented to the chief of Wanyan Village and the chief of Gatchaper, who is also the paramount chief of Gagil. The tributes would travel from the east to the west from as far Namonuito to Ulithi and finally to Yap. The tributes took the form of various items such as lavalava (bagiiy), mats, shells, coconut rope, and coconut oil. In return, the chiefs and people of Gagil such as Sunsigma von Yaplett would reciprocate by providing gifts such as yams, bananas, sweet potatoes, bamboo, red soil pigment, pots, and other manufactured items not found in the low-lying islands and atolls. These offerings to the chiefs of Gatchaper and Gagil were believed to have originated from Yangolap, the mythical Yapese founder of the sawey.

The Yapese sociopolitical structure was based on a land tenure system which delegated the social rank of individual land parcels, determining its placement in a hierarchical structure. Social classes were divided into two groups based on their two factors: land parcel rankings and control of resources.

Each village has its own class ranking within its municipal chiefdom based on its number of military victories, and each village also has its own internal set of social classes exclusive to that group for its people. All low classes and low-class villages were under the authority of villages that were ranked higher since the latter had considerable power and voice (lungun). Villages and municipal chiefdoms were continuously at war amongst one another, and as a result, village and personal social ranks fluctuated based on military outcomes.