Author and photographer Arlene Alda.
Author Parag Khanna discusses building American mega-regions.
PBS CEO Paula Kerger.
Grammy Award-nominated guitarist Ottmar Liebert.
Alexa Koenig, executive director of the Human Rights Center at University of California, Berkeley Law.
James Hansen, Columbia University's Earth Institute, talks about preserving the planet.
Nora Volkow, director of the National Institute on Drug Abuse, discusses opioid addiction and treatment.
Author Virginia Heffernan discusses her book 'Magic and Loss.'
Mexican conservationist Gerardo Ceballos discusses the decay of biodiversity.
Columnist Margaret Sullivan on the challenges of a free press.
Actor-director Rob Reiner discusses 'Being Charlie,' drugs and politics.
Martha Minow, dean of Harvard Law School, discusses America's legal system.
Author Michael Lynch discusses informed citizenship in the Internet age.
Anita Earls, Southern Coalition for Social Justice, discusses voter suppression at the polls.
Public health historian David Rosner talks about the water crisis in Flint, Mich.
Yale University scholar Wendell Wallach.
Smithsonian Institution historian Jon Grinspan.
Ernesto Zedillo, director of the Yale Center on Globalization.
Becca Heller, founder of the International Refugee Assistance Project.
Dan Cohen, director of the Digital Public Library of America.
GoDaddy CEO Blake Irving.
Ben Rattray, founder of Change.org.
Jaymee Messler, president of The Players' Tribune.
Chris Anderson, curator of TED.
Tom Frieden, director of Centers for Disease Control and Prevention, discusses combating addiction and disease.
Historian Eddie Glaude, Princeton University.
Claudia Juech, managing director of the Rockefeller Foundation.
Frank Farenkopf and Michael McCurry, co-chairmen of the Commission on Presidential Debates.
Laurie Glimcher, dean of Weill Cornell Medical College, talks about combating cancer.
Ernest Wilson, Dean of the Annenberg School for Communication and Journalism, talks about public broadcasting.
Television writer and producer Norman Lear.
Rabbi Jonathan Sacks.
Karenna Gore, director of the Center for Earth Ethics at Union Theological Seminary.
Author Salman Rushdie.
Music artist Moby talks about environmental consciousness.
Writer Jill Soloway, creator of 'Transparent,' discusses gender identity.
Annika Savill, Deputy Executive Head of the United Nations Democracy Fund.
Blues musician Guy Davis discusses his album 'Kokomo Kidd.'
Earth scientist Naomi Oreskes, Harvard University, discusses climate change.
William Pelgrin, former CEO of the Center for Internet Security, discusses cybersecurity.
Actor J.B. Smoove talks about the longevity of the comic.
President John Opdycke, Open Primaries, discusses non-partisan election systems.
Austin Beutner, former publisher of the Los Angeles Times, discusses the state of journalism.
Maria Freire, president of the Foundation for the National Institutes of Health, discusses medical research.
Author Salman Rushdie.
Szelena Gray, co-founder of Run for America.
Jeremy Ben-Ami, founder and president of J Street.
Mitchell E. Daniels Jr., president of Purdue University, discusses the link between college affordability and economic growth.
University of Hawaii professor Maya Soetoro-Ng, half-sister of President Barack Obama, talks about building a more peaceful society.
Alberto Ibarguen, president of the James L. Knight Foundation.
Novelist James Patterson.
Bob Graham, former chairman of the Senate Select Committee on Intelligence.
Elizabeth Spayd, editor in chief of Columbia Journalism Review, talks about innovations in journalism and technology.
Executive Director Louise Dubé, iCivics, discusses using virtual games to reinvigorate civics education for young people.
Michael Peterson of the Peter G. Peterson Foundation talks about solutions to national debt.
Dr. Carolyn Lukensmeyer, director of the National Institute for Civil Discourse.
CEO Gary Pruitt, The Associated Press, talks about keeping journalists safe.
The Rev. John Jenkins talks about moral education and incivility.
Professor Leah Wright, Harvard Kennedy School.
James Kats, Feld Professor of Emerging Media at Boston University's College of Communication.
Sue Gardner, former executive director of the Wikimedia Foundation, talks about the Internet.
Singer-songwriter Aloe Blacc.