This is a collection of primary sources. Most are historical.
Some will be linked in future to an online source of the original text.
There is another excellent bibliography at the University of Cambridge website. It is arranged by subject and contains mostly books on contemporary freethought.
Chronological
last updated 11-6-11
Brihaspati Sutra (600 BCE)
The Rise of the Moon Intellect (post-600 BCE)
Excerpts from Sarvadasanasamgraha (post-600 BCE)
Tattvopaplavasimha (post-600 BCE)
(Hsun Tzu, ca. 300-200 BCE)
Sovran Maxims (Epicurus, 341 - 270 BCE)
De Rerum Natura (Lucretius, 99 - 55 BCE)
De Natura Deorum - The Nature of the Gods (Cicero, 45 BCE)
On Divination (Cicero, 44 BCE)
Natural History (Pliny the Elder, 23 - 79)
Lun-Heng, or Discourses Weighed in the Balance (Wang Ch'ung, 27-97)
Meditations (Marcus Aurelius, 121 - 180)
Passing of Peregrinus (Lucian of Samosata, ca. 120 - 190)
Against the Physicists (Sextus Empiricus, ca. 150-225)
The Consolation of Philosophy (Anicius Manlius Severinus Boethius, 524)
The Book of the Emerald (Ibn al-Rawandi, ca. 850)
Against the Koran (Ibn al-Rawandi, ca. 850)
The Futility of Divine Wisdom (Ibn al-Rawandi, ca. 850)
The Prophet's Fraudulent Tricks (Abu Bakr al-Razi, 854 - 925)
The Strategems of Those Who Claim to be Prophets
Poems (Abdallah al-Ma'arri, 973 - 1057)
Deliverance from Error (Abu Hamid al-Ghazzali, ca. 1095)
The Bloudy Tenent of Persecution (Roger Williams, 1644)
Areopagitica: A Speech for the Liberty of Unlicensed Printing ... (John Milton, 1644)
Leviathan (Thomas Hobbes, 1651)
Christianity Not Mysterious (John Toland, 1696)
L'Histoire Naturelle de l'Ame (Julien Offray De LaMettrie, 1745)
L'Homme Machine (Julien Offray De LaMettrie, 1747)
A Free Inquiry into the Miraculous Powers (Conyers Middleton, 1749)
Christianisme Devoile (Paul-Henri Thiry, 1761)
The System of Nature (Paul-Henri Thiry, 1770)
An Enquiry Concerning Human Understanding, (David Hume, 17XX)
An Appeal to the Public for Religious Liberty (Isaac Backus, 1773)
Common Sense (Thomas Paine, 1776)
Dialogues concerning Natural Religion (David Hume, 1779)
Answer to Dr. Priestley's Letter to a Philosophical Unbeliever (Matthew Turner, 1782)
Dialogue Between a Priest and a Dying Man (Marquis de Sade, 1782)
Principles of Morals and Legislation (Jeremy Bentham, 1789)
Reason - The Only Oracle of Man (Ethan Allen, 1790)
The Rights of Man (Thomas Paine, 1791)
Les Ruines [English translation] (C. F. Volney, 1791)
Die Religion Innerhalb Der Grenzen Der Blossen Vernunft (Immanuel Kant, 1793)
The Age of Reason (Thomas Paine, 1793)
The Necessity of Atheism (Percy Bysshe Shelley, 1811)
Mails on the Sabbath (U.S. Senate, 1829)
Life of Jesus ( David Friedrich Strauss, 1835)
The Essence of Christianity (Ludwig Andreas Feuerbach, 1841)
Speech at 1852 Syracuse National Convention (Matilda Joslyn Gage, 1852)
The Origin of Species (Charles Darwin, 1859)
Evidence as to Man's Place in Nature (T. H. Huxley, 1863)
Science de l'Homme (Gustave Flourens, 1865)
History of the Rise and Influence of the Spirit of Rationalism in Europe (W. E. H. Lecky, 1865)
On the Progress of Education and Industrial Avocations for Women (Matilda Joslyn Gage, 1871)
Are We Christians? (Leslie Stephen, 1873)
Essays on Freethinking and Plain Speaking (Leslie Stephen, 1873)
Remarks of Susan B. Anthony at her Trial for Illegal Voting (Matilda Joslyn Gage, post-1873)
Three Essays on Religion (John Stuart Mill, 1874)
1876 Declaration of Rights (Matilda Joslyn Gage, 1876)
Right of Habeas Corpus (Matilda Joslyn Gage, 1876)
Woman A Mystery (Matilda Joslyn Gage, 1876)
The Gods, and Other Lectures (Robert Ingersoll, 1876)
Analysis of Religious Belief (John Russell, 1877)
Bible and Church Degrade Women (Elizabeth Cady Stanton, 1885)
Beyond Good and Evil
Robert Elsmere (Mrs. Humphrey Ward, 1888)
The Antichrist (Friedrich Nietzsche, 1988)
Why I am an Agnostic (Robert Ingersoll, 1896)
Woman in Newspapers (Matilda Joslyn Gage, 1881)
Woman as Inventor (Matilda Joslyn Gage, 1883)
Preceding Causes (Matilda Joslyn Gage, 18XX)
The Matriarchate; or Woman in the Past (Matilda Joslyn Gage, 18XX)
Men, Women, and Gods, and other Lectures (Helen H. Gardener, 1885)
Protest Against the Unjust Interpretation of the Constitution (Susan B. Anthony, et al., 1887)
Dangers of the Hour (Matilda Joslyn Gage, 1890)
Woman, Church and State (Matilda Joslyn Gage, 1893)
An Agnostic's Apology and Other Essays (Leslie Stephen, 1893)
In the Matter of the Cancellation of the Name of Matilda Joslyn Gage on Registry List of Election District (1894)
History of the Warfare of Science with Theology in Christendom (Andrew D. White, 1896)
The Truth about Jesus, Is He a Myth? (M. M. Mangasarian, 1909)
The Devil's Dictionary (Ambrose Bierce, 1911)
In Defense of Women (H. L. Mencken, 1918)
What I Believe (Bertrand Russell, 1925)
Why I am Not a Christian (Bertrand Russell, 1927)
Sceptical Essays (Bertrand Russell, 1928)
Atheism and Other Addresses (Joseph Lewis, 1930)
Rise and Fall of the Gods (Joseph McCabe, 1931)
The Forgery of the Old Testament (Joseph McCabe, 19xx)
Religious Lies (Joseph McCabe, 19xx)
Did Jesus Ever Live? (Joseph McCabe, 19xx)
Do We Need Religion? (Joseph McCabe, 19xx)
World Without Faith (John Beevers, 1935)
Is the Position of Atheism Growing Stronger? (Joseph McCabe, 1936)
The Value of Scepticism (Joseph McCabe, 19xx)
A Biographical Dictionary of Ancient, Medieval and Modern Freethinkers (Joseph McCabe, 1945)
Am I an Atheist or an Agnostic? (Bertrand Russell, 1949)
What is an Agnostic? (Bertrand Russell, 1953)
Messiah (Gore Vidal, 1954)
Julian (Gore Vidal, 1964)
Selected Letters [of H. P. Lovecraft] (Donald Wandrei, ed., 1965-1976)
An Atheist Epic (Madalyn Murray O'Hair, 1970, rev. ed. 1989)
A Short History of Atheism (James Thrower, 1971)
Scepticism (Kai Nielsen, 1973)
Freedom under Siege: The Impact of Organized Religion on Your Liberty and your Pocketbook
We Become Atheists (Gora, 1975)
Ethics: Inventing Right and Wrong (J. L. Mackie, 1977)
Jesus the Magician (Morton Smith, 1978)
Atheism: The Case Against God (George E. Smith, 1979)
The History of Skepticism from Erasmus to Spinoza (Richard H. Popkin 1979)
The Alternative Tradition: Religion and the Rejection of Religion in the Ancient World (James Thrower, 1980)
Creation (Gore Vidal, 1981)
The Sources of Modern Atheism (Marcel Neusch, 1977, trans. from French 1982)
Philosophy and Atheism: In Defense of Atheism (Kai Nielsen, 1985)
The Encyclopedia of Unbelief (Gordon Stein, ed., 1985)
The Transcendental Temptation: A Critique of Religion and the Paranormal (Paul Kurtz, 1986)
Who Wrote the Bible? (Richard Elliott Friedman, 1987)
Gospel Fictions (Randel Helms, 1988)
God, Scepticism and Modernity (Kai Nielsen, 1989)
Ethics Without God (Kai Nielsen, 1990)
God and the Grounding of Morality (Kai Nielsen, 1991)
Losing Faith in Faith: From Preacher to Atheist (Dan Barker, 1992)
Live from Golgotha (Gore Vidal, 1992)
The New Skepticism: Inquiry and Reliable Knowledge (Paul Kurtz, 1992)
The Lost Gospel: The Book of Q and Christian Origins (Burton Mack, 1993)
No Longer Awash in Religion (Catherine Fahringer, 1994)
Living Without Religion: Eupraxsophy (Paul Kurtz, 1994)
Challenges to the Enlightenment: In Defense of Reason and Science (Paul Kurtz and Tim Madigan, eds., 1994)
Encounter with Reality: Children's Reactions on Discovering the Santa Clause Myth, Child Psychiatry & Human Development
25:2:67-84 (Carl J. Anderson and Norman M. Prentice, 1994)
The Demon-Haunted World: Science as a Candle in the Dark (Carl Sagan, 1995)
The Encyclopedia of Biblical Errancy (C. Dennis McKinsey, 1995)
The Missionary Position: Mother Teresa in Theory and Practice (Christopher Hitchens, 1995)
The Jesus Legend (G. A. Wells, 1996)
Who Wrote the New Testament? The Making of the Christian Myth (Burton Mack, 1996)
2000 Years of Disbelief: Famous People with the Courage to Doubt (James A. Haught, 1996)
Arguing for Atheism: An Introduction to the Philosophy of Religion (Robin Le Poidevin, 1996)
Thought Contagion: How Belief Spreads Through Society (Aaron Lynch, 1996)
Philosophy Atheism (Kai Nielsen, 1996)
At Cross Purposes (Catherine Fahringer, 1997)
Out of the Desert?: Archaeology and the Exodus/Conquest Narratives (William H. Stiebing, 1998)
Nonbelief and Evil: Two Arguments for the Nonexistence of God (Theodore M. Drange, 1998)
The Respectibility of Belief (Catherine Fahringer, 1998)
What is Atheism?: A Short Introduction (Douglas E. Krueger, 1998)
L'Atheisme (Alexandre Kojeve and Laurent Bibard, 1998)
How We Believe: The Search for God in an Age of Science (Michael Shermer, 1999)
Western Atheism: A Short History (James Thrower, 1999)
The Jesus Mysteries (Timothy Freke, 1999)
Who's Who in Hell (Warren Allen Smith, 2000)
An Intelligent Person's Guide to Atheism (Daniel Harbour, 2001)
Skepticism and Humanism: The New Paradigm (Paul Kurtz, 2001)
Letters to a Young Contrarian (Christopher Hitchens, 2001)
Skeptical Odysseys (Paul Kurtz, ed., 2001)
Religion Explained: The Evolutionary Origins of Religious Thought (Pascal Boyer, 2001)
Why God Won't Go Away: Brain Science and the Biology of Belief (Andrew Newberg, Eugene D'Aquili and V. Rause, 2001)
Can We Be Good Without God? (Robert Buckman, 2002)
In Gods We Trust: The Evolutionary Landscape of Religion (Scott Atran, 2002)
H. L. Mencken on Religion (S. T. Joshi, ed., 2002)
Atheism: A Very Short Introduction (Julian Baggini, 2003)
What is Good?: The Search for the Best Way to Live (A.C. Grayling, 2003)
A Devil's Chaplain (Richard Dawkins, 2003)
God's Defenders: What They Believe and Why They are Wrong (S. T. Joshi, 2003)
The History of Skepticism from Savanorala to Bayle (Richard H. Popkin, 2003)
How Mumbo Jumbo Conquered the World (Francis Wheeler, 2004)
The God Gene: How Faith is Hardwired into Our Genes (Dean Hamer, 2004)
Why Intelligent Design Fails: A Scientific Critique of the New Creationism (Matt Young and Taner Edis, 2004)
Cambridge Companion to Atheism (Michael Martin, ed., 2005)
Laughing Jesus (Timothy Freke, 2005)
Dictionary of Atheism, Skepticism, and Humanism (Bill Cooke, ed., 2005)
The God Delusion (Richard Dawkins, 2006)
The Quotable Atheist (Jack Huberman, 2006)
Breaking the Spell: Religion as a Natural Phenomenon (Daniel Dennett, 2006)
Flock of Dodos: Behind Modern Creationism, Intelligent Design and the Easter Bunny (Barrett Brown & Joe Alston, 2007)
Letter to a Christian Nation (Sam Harris, 2007)
God is Not Great: How Religion Poisons Everything (Christopher Hitchens, 2007)
The Atheist Manifesto: The Case Against Christianity, Judaism and Islam (Michel Onfray, 2007)
God: The Failed Hypothesis (Victor Stenger, 2007)
The Portable Atheist (Christopher Hitchens, ed., 2007)
God on Trial: Landmark Cases from America's Religious Battlefields (Peter Irons, 2007)
Good Without God: What a Billion Non-religious People Do Believe (Greg M. Epstein, 2009)
The Moral Landscape (Sam Harris, 2010)
The Unbelievers: The Evolution of Modern Atheism (S. T. Joshi, 2011)