Works, Archives Hub: Oakeshott, Michael Joseph, Biography.com: Oakeshott, Michael Joseph, Books in Review: The Politics of Faith & the P, Michael Oakeshott, Michael Oakeshott and the Political Economy of Fre, Michael Oakeshott Association

Peter John Olivi, Peter John Olivi, Questions on the Sentences, The Olivi Page

Catholic Encyclopedia: Nicole Oresme, History of Calculus: Oresme, Nicole, On the Book of the Heavens and the World of Arist, Oresme, World of Scientific Biography: Oresme, Nicole

Biography.com: Ortega y Gasset, Jose, Books and Writers: José Ortega y Gasset, Columbia Encyclopedia: Ortega y Gasset, Jose, History Guide: Ortega y Gasset, Jose? Ortega y Gasset, Liberal Thinkers: José Ortega y Gasset, Revolt of the Masses, The Expository Philosopher: Ortega y Gasset, Thoughts on Technology

Biography.com: Otto, Rudolf, Friesian School: Rudolf Otto, Mysticism Defined by Rudolf Otto, Rudolf Otto (1869-1937), Rudolf Otto in Rem B. Edwards