The Herbert and Katherine Jacobs Second House, or Jacobs II, is a Frank Lloyd Wright home in Madison, Wisconsin, built from 1946 to 1948 as an innovative response to the Jacobs family’s rural farm setting. With its semicircular plan, earth-bermed north side, and glass-lined south face, the house became an important early experiment in passive solar design and organic building. Construction was difficult and delayed, and Herbert and Katherine Jacobs helped build it themselves, even moving into the root cellar before the house was finished. Later preserved by subsequent owners, it gained recognition for its bold form and historic architectural significance.