The Three Essays on Religion were written at different times during Mill's life, and only published after his death. The first two, 'Nature' and 'The Utility of Religion' date from the 1850s - the period between the publication of 'The Principles of Political Economy' and 'On Liberty'. The third longer essay, 'Theism' was written between 1868 and 1870. The three essays were published posthumously in 1874.