The author presents an overview of the skeptical tradition against which the work of Descartes must be understood. Specific thinkers discussed include Sextus Empiricus, Marcus Tullius Cicero, Michel Montaigne, Pierre Charron, and Al-Ghazâlî. Some attention is also paid to standard anti-skeptical replies available in Descartes’s time and place, including discussions of the work of John Buridan and Albert of Saxony.