Actress Daryl Hannah is arrested by U.S. Park Police in front of the White House in Washington, D.C., Aug. 30, 2011, during a protest against the Keystone oil pipeline.Photos: Daryl Hannah Arrested
Credit: AP Photo/Evan Vucci
Since an earthquake struck Haiti in January 2010, Sean Penn has been an outspoken supporter of relief efforts there and has traveled to the country several times.
Photo: Penn leaves a six-month remembrance ceremony, July 12, 2010, in Port-Au-Prince, Haiti.
Credit: THONY BELIZAIRE/AFP/Getty Images
Alicia Silverstone is a conservationist who has sworn off a diet including meat and dairy products. She wrote a book called "The Kind Diet," has a website called "The Kind Life" and was voted PETA's "sexiest vegetarian alive" in 2004.
Photo: Silverstone attends the Los Angeles premiere of Francis Ford Coppola's" Tetro," held at the Billy Wilder Theater within the Hammer Museum in Westwood, Calif., June 3, 2009.
Credit: AP Photo
Ed Begley, Jr.
Actor and environmental activist talks about green car design at the 2011 Forward with Ford tech conference.
Credit: Ford Motor Company
Kim Basinger has worked with the Performing Animal Welfare Society.
Photo: Basinger, a cast member of "8 Mile," waves to fans as she arrives at a screening of the film Nov. 6, 2002, in Los Angeles.
Danny Glover has been an outspoken critic of the Iraq War since its beginning. In 1999, he filed a formal complaint with New York's Taxi and Limousine Commission claiming drivers deliberately failed to pick him up. In 2008, he supported California's Proposition 7, which would have required the state to get 50 percent of its power from renewable resources by 2025.
Photo: Danny Glover, left, is arrested by Montgomery County Police as Service Employees International Union president Andy Stern cheers Glover on during a protest by the SEIU of Sodexo headquarters in Gaithersburg, Md., Friday, April 16, 2010.
Credit: AP Photo/Jacquelyn Martin
Susan Sarandon was appointed a UNICEF Special Representative in 1999. She's been active in many causes, beginning with protesting the Vietnam War. She has supported the Green Party and occasionally used her time at awards shows to talk about issues she finds important.
Photo: Sarandon presents an award to actor Harvey Keitel as a tribute to his career at the 10th Marrakech International Film Festival in Marrakech, on Dec. 8, 2010.
Credit: ABDELHAK SENNA/AFP/Getty Images
Alec Baldwin has supported a variety of causes, including environmentalism, animal rights, campaign finance reform and gun control.
Photo: Baldwin speaks on the need for continued funding of the arts at the Arts Advocacy Day Congressional Arts Kick-off on April 5, 2011, in Washington, D.C.
Credit: Paul Morigi/Getty Images
Viggo Mortensen told the St. Lawrence University - his alma mater - class of 2006 that "activism is not a dirty word."
He encouraged the graduates to get involved in the United States' health care system.
Photo: Viggo Mortensen arrives for the premiere of "The Road" during the Times BFI 53rd London Film Festival at the Vue West End on Oct. 16, 2009, in London.
Credit: Samir Hussein/Getty Images
Jane Fonda has supported a variety of causes throughout her career, starting with opposition to the Vietnam War which earned her the nickname Hanoi Jane.
Photo:: Jane Fonda arrives at UCLA Longevity Center's 20th Anniversary ICON Awards on June 4, 2011 in Beverly Hills, Calif.
Credit: Jerod Harris/Getty Images
Richard Gere, a Buddhist, has supported Tibet in its struggles with the Chinese government and worked with AIDS organizations in India, among other causes.
Photo: Gere attends the Museum of the Moving Image salute to Alec Baldwin at Cipriani 42nd Street on Feb. 28, 2011, in New York.
Credit: Stephen Lovekin
Matt Damon has championed several causes. In late July, he got into an argument with a reporter from reason.tv at the Save Our Schools march in Washington, D.C., in which he took issue with the reporter's reasoning behind teacher incentives.
Photo: Matt Damon attends the 6th annual Made In NY Awards at Gracie Mansion on June 6, 2011, in New York.
Credit: Gary Gershoff/Getty Images
Mary Tyler Moore
Mary Tyler Moore has long been a supporter of animal rights.
Photo: Mary Tyler Moore, left, and Bernadette Peters hold adoptable dogs at The Pedigree Dogstore in New York, Feb. 21, 2008.
Joaquin Phoenix has been a vocal supporter of People for the Ethical Treatment of Animals and has appeared in some of their videos.
Photo: Phoenix arrives at PETA's 30th Anniversary Gala and Humanitarian Awards in Los Angeles on Sept. 25, 2010.
Credit: AP Photo/Matt Sayles
Robert Redford is a conservationist and a trustee of the Natural Resources Defense Council.
Photo: Sundance Institute founder and president Robert Redford speaks at the Day 1 Press Conference during the 2011 Sundance Film Festival at the Egyptian Theatre on Jan. 20, 2011, in Park City, Utah.
Credit: Jemal Countess/Getty Images
Pierce Brosnan promotes whale conservation campaigns and has been involved with International Fund for Animal Welfare and the Natural Resources Defense Council.
Photo: Brosnan walks from the West Wing of the White House in Washington, D.C., May 19, 2009, after attending a meeting there.