The Will Geer Theatricum Botanicum, named for the English botanist John Parkinson's herbal, Theatrum Botanicum (1640), is an open-air theater founded in Topanga Canyon, near Santa Monica, California by Will Geer in 1973. His former wife, Herta Ware, helped develop the outdoor summer theatre and continued to appear in plays there after her husband's death in 1978. The company features Shakespeare, as well as modern and contemporary authors. The theater, set in the natural amphitheater of a mountain canyon, is also used for occasional concerts.

Will Geer combined his acting and botanical careers at the Theatricum, by making sure that every plant mentioned in Shakespeare was grown there.