On the Improvement of the Understanding

Lectures of Col. R. G. Ingersoll, Volume I Including His Answers to the Clergy, His Oration at His Brother's Grave, Etc., Etc.

Philosophy and Religion Six Lectures Delivered at Cambridge

Flowers of Freethought (First Series)

Heretics And Heresies From 'The Gods and Other Lectures'

Humboldt From 'The Gods and Other Lectures'

The Works of Robert G. Ingersoll, Vol. 06 (of 12) Dresden Edition—Discussions

Christianity Unveiled Being an Examination of the Principles and Effects of the Christian Religion

The Bible: I. Authenticity II. Credibility III. Morality

Meditations on the Actual State of Christianity, and on the Attacks Which Are Now Being Made Upon It.

Die Religion innerhalb der Grenzen der bloßen Vernunft Text der Ausgabe 1793, mit Beifügung der Abweichungen der Ausgabe 1794