The Enlightenment has been defined in many different ways. Even in the eighteenth century, contemporaries were well aware that when an Italian called this movement of ideas Illuminismo, he meant something other than the word Lumières which would have been used by a friend in France, or the Aufklärung current in the German states. With such diversity, it was no wonder that the Berlin pastor Johann Friedrich Zollner (1753–1824) in an article in the December 1783 number of the Berlinische Monatsschrift should have asked ‘What is Enlightenment? This question is nearly as important as the question What is truth? This question must be answered before anyone can begin to enlighten themselves. And yet I have never seen it answered anywhere!’ This question, hidden away in a footnote to an article on matrimonial law by an obscure pastor, was one of the most fruitful ever asked. Essays in answer to it began to be submitted to the Monatsschrift by leading thinkers. For the Jewish philosopher Moses Mendelssohn (1729–86), who published an essay in the September number in 1784, ‘Enlightenment’ referred to an as yet uncompleted process of education in the use of reason, which should be open to all. Mendelssohn therefore supported the movement for ‘popular philosophy’ which sought to spread Enlightenment ideas among lower social classes. Other competitors, such as Schiller, Herder, Wieland, Hamann, Riem and Lessing, some of the great names of the German Enlightenment, put forward quite different ideas, often, as did Schiller, emphasising aesthetics as defining the Enlightenment. These essays can be read as a compendium of the diverse meanings which by the end of the century had come to be attached to the word ‘Enlightenment’.