, Probab. Statist. Group Manchester (21 pp) Let X = (X t ) t≥0 be a strong Markov process, and let G 1 , G 2 and G 3 be continuous functions satisfying G 1 ≤ G 3 ≤ G 2 and E x sup t |G i (X t )| < ∞ for i = 1, 2, 3 . Consider the optimal stopping game where the sup-player chooses a stopping time τ to maximise, and the inf-player chooses a stopping time σ to minimise, the expected payoffwhere X 0 = x under P x . Define the upper value and the lower value of the game bywhere the horizon T (the upper bound for τ and σ above) may be either finite or infinite (it is assumed thatIf X is right-continuous, then the Stackelberg equilibrium holds, in the sense that V * (x) = V * (x) for all x with V := V * = V * defining a measurable function. If X is right-continuous and left-continuous over stopping times (quasi-left-continuous), then the Nash equilibrium holds, in the sense that there exist stopping times τ * and σ * such thatfor all stopping times τ and σ , implying also that V (x) = M x (τ * , σ * ) for all x . Further properties of the value function V and the optimal stopping times τ * and σ * are exhibited in the proof.