We have witnessed in recent years a revival of conjectural variations in game theory. This reincarnation of an old idea, taking a dynamic point of view, aims at combining factual adequacy with the requirements of a firmly grounded theory. This book presents, for the first time, a comprehensive account of conjectural variations equilibria in their static inceptions, featuring new comparative results of equilibria with regard to efficiency. It then describes several advances in dynamic game theory, allowing one to understand conjectural variations equilibria as dynamic equilibria. The question of conjectures and their evolution in game-theoretic and learning situations is also discussed.