Lilly Endowment Inc., headquartered in Indianapolis, Indiana is one of the world's largest private philanthropic foundations and is among the ten largest such endowments in the United States.

The endowment was founded in 1937 by J. K. Lilly Sr. and his sons Eli and J. K. Jr., with gifts of stock in the pharmaceutical company Eli Lilly and Company. While stock in the company is the Endowment's foremost asset, the Endowment is separate from the company. The Endowment, a private foundation, is in a different location, has a different board of directors, and is not linked to the company, except for the significant percentage of the company's stock it holds. The foundation has historically had three primary areas of grantmaking: community development, education and religion. Lilly Endowment is unique in that it is the largest private foundation in the United States that funds almost exclusively in its home city and state.