The Susquehannock, also known as the Conestoga, Minquas, and Andaste, were an Iroquoian people who lived in the lower Susquehanna River watershed in what is now Pennsylvania. Their name means “people of the muddy river.”

The Susquehannock were first described by John Smith, who explored the upper reaches of the Chesapeake Bay in 1608. The Susquehannocks were active in the fur trade and established close trading relationships with Virginia, New Sweden, and New Netherland. They were in conflict with Maryland until a treaty was negotiated in 1652, and were the target of intermittent attacks by the Haudenosaunee (Iroquois).

By the 1670s, their population had declined sharply as a result of disease and war. The Susquehannock abandoned their town on the Susquehanna River and moved south into Maryland. They erected a palisaded village on Piscataway Creek, but in September 1675, the Susquehannock were besieged by militias from Maryland and Virginia. The survivors of the siege scattered, and those who returned to the north were absorbed by the Haudenosaunee.

In the late 1680s, a group of Susquehannock and Seneca established a settlement on the Conestoga River in present-day Lancaster County, Pennsylvania, where they became known as the Conestoga. The population of this community gradually declined, and in 1763, the last members were massacred by the vigilante group known as the Paxton Boys. While there are a significant number of Indigenous people alive today of Susquehannock ancestry, including citizens of the Seneca–Cayuga Nation in Oklahoma and the Six Nations of the Grand River First Nation in Ontario, the Susquehannock as a distinct cultural entity are considered extinct.

The Susquehannock were an Iroquoian-speaking people. Little of the language has been preserved. The chief source is the Vocabula Mahakuassica compiled by the Swedish missionary Johannes Campanius during the 1640s. Campanius's vocabulary contains about 100 words and is sufficient to show that Susquehannock is a Northern Iroquoian language, closely related to the languages of the Haudenosaunee and in particular that of the Onondaga. The language is considered extinct as of 1763 when the last remnant community of the Susquehannock was massacred at Lancaster, Pennsylvania.

The Europeans who colonized the Mid-Atlantic coast of North America typically adopted the names that were used by the coastal Algonquian-speaking peoples for interior tribes. The Europeans adapted and transliterated these exonyms to fit their own languages and spelling systems, and tried to capture the sounds of the names. What the Susquehannock called themselves is not known.

In the late 15th and early 16th centuries the Susquehannock lived in scattered hamlets on the North Branch of the Susquehanna River in what is now Bradford County, Pennsylvania, and Tioga County, New York. Of Northern Iroquoian ancestry, the Susquehannock became culturally and linguistically distinct before 1500.

A southward migration towards the Chesapeake Bay began in the second half of the 16th century, possibly the result of conflict with the Haudenosaunee to the north. The shortening of the growing season during the Little Ice Age, and the desire to be closer to sources of trade goods may also have been factors. The Susquehannock assimilated the Shenks Ferry people in the lower Susquehanna River valley, and established a palisaded village in present-day Lancaster County, Pennsylvania. An archaeological excavation in 1931 revealed that the village (known as the Schultz Site) contained at least 26 longhouses. The Schultz site was largely abandoned c. 1600 due to overcrowding and depletion of local resources. A larger fortified town was constructed near what is today Washington Boro. The town is estimated to have been 250,000 square feet in size with a population of about 1,700 people.