A strict determinism has always been considered a crucial part of the Stoic doctrine. Seneca, however, the most important Roman stoic, never produced a systematic description of Fatum. This article presents, in the first part, a synthetic discussion of the main remarks contained in single works of Seneca, which in my view are in accordance with the mainstream Stoicism, though the philosopher’s interests seem to lie primarily in the psychological aspects, related to the acceptance of Fatum and in the reconciliation of fate and morality. In the second part, I try to assess the remaining reasons of interest that the thought of Seneca and the Stoic doctrine can still present in the modern world and for an audience of non specialists, considering the astonishing progresses realized in the recent years by the Neurosciences in the evaluation of the brain’s decision making. Because free will is so closely related to the concept of moral responsibility, our current codes of ethics assume that our choices must be free. Some results of experimental studies cast a shadow on the human freedom but much remains to be discovered and, in the meantime, we are probably better off believing in it anyway.