The IVth Symposium Platonicum was entirely given over to a study of Plato's Timaeus and Critias. The papers published here deal both with more traditional problems of interpretation - whether or not the universe had a beginning in time, the status of the demiurge, the relation between the Timaeus and the Critias - and with a range of questions less frequently discussed, i.e. the treatment in the Timaeus of mathematics, of cosmic providence, sense-perception, medicine, the relation between soul and body, the literary genre of the Critias, the political project of the two dialogues.