One Capital Center, Office skyscraper in downtown Boise, US

One Capital Center is a 14-floor, 206-foot office tower at 999 Main Street in downtown Boise, built in 1975 in a modernist style. It was the tallest building in Boise and Idaho until 1978, when US Bank Plaza overtook it; it now ranks fourth in the city.

Mountain Bell built this tower in 1975 as one of Boise's first modern office buildings, signaling the city's push toward downtown redevelopment. The project marked a turning point when Boise began to reshape its downtown with contemporary architecture.

The building's name comes from its site at 999 Main Street, a block tied to Boise's civic center. Its most noted tenant was billionaire J. R. Simplot (1909–2008), the Idaho potato and agribusiness magnate, who kept an office on the 13th floor. Since 2009 a webcam has followed a pair of peregrine falcons nesting on the top floor, drawing bird watchers.

The building sits in the heart of downtown Boise and is easy to reach on foot from the main streets. The ground-floor dining spaces welcome walk-in visitors and offer convenient options for lunch or a quick meal.

In 2009 a webcam recorded a pair of peregrine falcons nesting on the 14th floor of this office tower, and four eggs were being incubated in the nest. The feed drew bird watchers who followed the birds online. Billionaire J. R. Simplot (1909–2008) kept an office on the 13th floor.