The Unbelievers explores the debate surrounding creationism versus evolution, and advocates the importance of scientific thought and reason in a modern world. Scientists Richard Dawkins and Lawrence Krauss speak publicly around the globe, encouraging others to reject religious and politically motivated approaches toward what they think to be important current issues. The documentary features appearances by Stephen Hawking, Ayaan Hirsi Ali, Sam Harris, Cameron Diaz, Woody Allen, Penn Jillette, Ian McEwan, and David Silverman.