Ventura, officially named San Buenaventura (Spanish for "Saint Bonaventure"), is a city in and the county seat of Ventura County, California, United States. It is a coastal city located northwest of Los Angeles. The population was 110,763 at the 2020 census. Ventura is a popular tourist destination, owing to its historic landmarks, beaches, and resorts.

Ventura has been inhabited by different peoples, including the Chumash Native Americans, for at least 10,000 years. With the arrival of Spanish missionaries in 1782, Mission San Buenaventura was established by Junípero Serra, giving the city its name. Following the Mexican secularization of the Californian missions, San Buenaventura was granted by Governor Pío Pico to Don José de Arnaz as Rancho Ex-Mission San Buenaventura and a small community arose. Following the American Conquest of California, San Buenaventura was eventually incorporated as a city in 1866. The 1920s brought a major oil boom which significantly developed and expanded Ventura, a growth that continued with the post–World War II economic expansion.

Archaeological discoveries in the area suggest that humans have populated the region for at least 10,000–12,000 years. Archaeological research demonstrates that the Chumash people have deep roots in central and southern coastal regions of California, and has revealed artifacts from their culture. Shisholop Village, designated Historic Point of Interest #18 by the city, was the site of a Chumash village. They had keen oceanic navigational skills made use of the abundant local resources from sea and land. The Ventura Chumash were in contact with the Channel Islands Chumash; both mainland and island Chumash utilized large plank-sewn seagoing canoes, called Tomol, with the island people bringing shell bead money, island chert, and sea otter pelts to trade for mainland products like acorns and deer meat.

In 1769, the Spanish Portolà expedition, first recorded European visitors to inland areas of California, came down the Santa Clara River Valley from the previous night's encampment near today's Saticoy and camped near the outlet of the Ventura River on August 14. Fray Juan Crespi, a Franciscan missionary traveling with the expedition, noted that "we saw a regular town, the most populous and best laid-out of all that we had seen on the journey up to the present time." Archaeological records found that the Chumash village they encountered was settled sometime around AD 1000. Junípero Serra, first leader of the Franciscans in California, founded Mission San Buenaventura in 1782 as his ninth and last mission established near the Chumash village as part of Spain's colonization of Alta California. The mission was named for St. Bonaventure, a 13th-century Franciscan saint and a Doctor of the Church. San Miguel Chapel was the first outpost and center of operations while the first Mission San Buenaventura was being constructed. The first mission burned in 1801 and a replacement building of brick and stone was completed in 1809. The bell tower and facade of the new mission was destroyed by an 1812 earthquake. The Mission was rebuilt and functions as a parish church.

The Mexican secularization act of 1833 was passed twelve years after Mexico won independence from Spain in 1821. Mission land was sold or given away in large grants called ranchos. Rancho Ex-Mission San Buenaventura was a 48,823-acre (197.58 km²) grant that included downtown Ventura. The Battle of San Buenaventura was fought in 1838 between competing armies from northern and southern California. Governor Juan Bautista Alvarado granted Rancho San Miguel to Felipe Lorenzana and Raymundo Olivas, whose Olivas Adobe on the banks of the Santa Clara River was the most magnificent hacienda south of Monterey. Fernando Tico also received a Mexican land grant for Ojai and a parcel near the river in downtown Ventura.

Following the American Conquest of California in the Mexican–American War, California became a U.S. territory in 1848 and a U.S. state in 1850. After the American Civil War, settlers came to the area, buying land from the Mexicans, or simply as squatters. Vast holdings were later acquired by Easterners, including railroad magnate Thomas A. Scott. He sent Thomas R. Bard to handle Scott's property.

Ventura had a flourishing Chinese settlement in the early 1880s. The largest concentration of activity, known as China Alley, was just across Main Street from the Mission San Buenaventura.

Ventura Pier was built in 1872 at a cost of $45,000 and was the longest wooden pier in California. By 1917, it had been rebuilt to a length of 1,700 feet (520 m). Much of the pier was destroyed by a storm in 1995, but it was subsequently rebuilt.