Tualatin (properly pronounced 'twälə.tun in English) was the name of a collection of related but independent villages whose members spoke a dialect of Northern Kalapuya, the northernmost of three languages composing the Kalapuyan language-family. Synonyms include Atfalati, Tfalati, and Twalati (variously spelled).

Sixteen Tualatin villages are known by name: these stretched through Tualatin Plains (modern-day Beaverton, Hillsboro, Mountaindale, Forest Grove), the Wapato Valley (Gaston), and the Chehalem and North Yamhill Valleys (Newberg, Carlton, Yamhill). Eight of these villages were clustered around Wapato Lake, a former marshy lake at Gaston noted for its abundance of wapato (Sagittaria latifolia), the tubers of which were an important Native staple food.

Tualatins lived about half the year in dirt-banked, semi-excavated winter houses built of cedar-bark slabs or cedar planks lashed to a rectangular framework. They spent the drier part of the year camped across their tribal territory in pursuit of game, fish, and a variety of roots, seeds, and berries. By carefully preserving and storing these provisions, Tualatins had time during the winter months for storytelling, religious ceremonialism, as well as household tasks such as tool making and basket weaving.

The basic unit of Tualatin society was the autonomous winter village, consisting of one to several extended families each tracing kinship through the male line.  Women usually married into this group from outside. Larger villages had one or more chiefs, who with their immediate families were distinguished by the quality of their apparel and the value of their property. Property included slaves who lived in the household with their masters.  Slave status was hereditary, and slaves were not permitted to subject their infants' heads to frontal-occipital flattening, the mark of free birth among lower Columbia Native people.

Tualatin religion revolved around the individual's relationship with one or more helpful spirits, first sought on pre-adolescent quests and expressed in later life through songs performed at winter spirit-dances. Individuals having relationships with particularly strong spirits might become shamans, called on to treat more serious illnesses.

Tualatins suffered greatly from introduced diseases. Only about sixty-five still survived in 1855, when the U.S. government concluded a treaty with all of the Willamette Valley tribes. In 1856, the tribe was removed to Grand Ronde Reservation, some sixty miles southwest of their original homeland. Descendants of the Grand Ronde Tualatins continue to live in the Grand Ronde area and in other Native communities of the Pacific Northwest.