The Santa Clara Valley (Spanish: Valle de Santa Clara) is a geologic trough in Northern California that extends 90 miles (140 km) south–southeast from San Francisco to Hollister. The longitudinal valley is bordered on the west by the Santa Cruz Mountains and on the east by the Diablo Range; the two coastal ranges meet south of Hollister. The San Francisco Bay borders the valley to the north, and fills much of the northern third of the valley. The valley floor is an alluvial plain that formed in the graben (tectonic depression) between the San Andreas Fault to the west and the Hayward and Calaveras faults to the east. Within the valley and surrounding the bay on three sides are the urban communities of San Mateo County, Santa Clara County, and Alameda County, while the narrow southern reaches of the valley extend into rural San Benito County to Hollister. In practical terms, the central portion of the Santa Clara Valley is often considered by itself, contained entirely within Santa Clara County.

The valley, named after the Spanish Mission Santa Clara, was for a time known as the Valley of Heart's Delight for its high concentration of orchards, flowering trees, and plants. Until the 1960s it was the largest fruit-producing and packing region in the world, with 39 canneries. The growing high-tech industry in the 1960s transformed the area from farmland to densely populated cities, and it became referred to as Silicon Valley.

Once primarily agricultural because of its highly fertile soil, Santa Clara Valley is now largely urbanized, although its far southern reaches south of Gilroy remain agrarian. Few traces of its agricultural past can still be found, but the Santa Clara Valley American Viticultural Area remains a large wine-making region. It was one of the first commercial wine-producing regions in California (and possibly the United States), utilizing high-quality French varietal vines imported from France.

The northern end of the Santa Clara Valley is at San Francisco, and the southern end is south of Hollister. The valley is bounded by the Santa Cruz Mountains on the southwest, which separate the valley from the Pacific Ocean, and by the Diablo Range on the northeast. The valley is approximately 93 miles (150 km) long by 15 miles (20 km) wide. Its largest city is San Jose. Santa Clara Valley has a Mediterranean semi-arid climate.

Joseph S. Diller, a geologist, observed in 1915 that a "notable peculiarity" of the Santa Clara Valley is that "it is divided transversely by a scarcely noticeable soil-covered divide." The northern portion is drained northward by various rivers and creeks into San Francisco Bay. The southern portion of the valley is drained southward by Llagas Creek into the Pajaro River, which in turn flows westward to Monterey Bay. As one travels across the valley floor, "the alluvial plain is continuous across the divide." The summit of the transverse divide is about two miles from the former town of Madrone at an elevation of 345 feet (105 meters), but the alluvial plain is so continuous that most travelers are unaware they are crossing between two drainage basins.

The earliest known inhabitants on the Santa Clara Valley are the Ohlone people, who had eight distinct languages and tribes in the coastal region. Mission Santa Clara de Asís, which had control over a vast tract of land stretching from Palo Alto to Gilroy, was founded by Franciscans in 1777. San Jose was California's first town and was also founded in 1777 by Spain as an agricultural pueblo. There were 66 original settlers. In Spanish and Mexican times the land was devoted to cattle, as was most of California. Following the Mexican–American War San Jose was briefly the capital of California. The influx of Americans resulted in relocation of many of the native Mexican and Indian people of San Jose to the mission at Santa Clara, which had been under control of Jesuits from 1850; they founded Santa Clara University there in 1851. In 1860, as an American town, the population of San Jose was 4,579, with cattle ranching still the main agricultural activity. For a time wheat became the main crop, but in the 1870s fruit gradually became the main crop and processing of fruit by drying or canning the predominant industry. The railroad reached San Jose in 1860.

The valley with its scenic beauty, mild climate, and thousands of acres of blooming fruit trees was known as "The Valley of Heart's Delight". Various fruit cooperatives were formed in the area to deal with economic issues, including the California Fruit Union (founded in 1883) and the Santa Clara County Fruit Exchange (founded in 1892). Prunes were a major crop, with the valley was producing the majority of prunes in California by 1900 and shipped internationally. Water was supplied from an artesian aquifer and when the water table dropped, wells were pumped. Many orchards were small with housing and fruit growing in a dispersed pattern. By the 1920s and 1930s, the agricultural and horticultural industries were doing well in the valley and included 18 canneries, 13 dried-fruit packing houses, and 12 fresh-fruit and vegetable shipping firms, and they were shipping internationally. Del Monte and Sunsweet are two brands which originated in the Santa Clara Valley.^{[citation needed]}

The need for workers greatly exceeded the local population and in the nineteenth century, Chinese and Japanese immigrants met that need. Toward the end of the nineteenth century many Italians and other immigrants from Southern and Eastern Europe came to the valley and worked in the orchards and canneries. During the 20th century there were Filipino immigrants and increasing numbers of immigrants from Mexico who during World War II became the dominant agricultural workforce. The town of San Jose was dominated by its business community, which was in part composed of Irish Catholics, who had a self-contained social life which did not include immigrant labor. There was marked prejudice against Asians, particularly Chinese, who gradually left the valley.