To mark the 60th anniversary of the United Nations' founding, the Office of the President and the College of Letters, Arts & Social Sciences are hosting a lecture on "The United Nations and the Challenges of the 21st Century" by Gillian Sorensen, senior adviser and national advocate at the U.N. Foundation. Free and open to the public, the discussion begins at noon on Thursday, Nov. 17, in the Bronco Student Center, Ursa Minor Suite.