1. Introduction. 1.1. Questions about model uncertainty. 1.2. Ten papers about model uncertainty -- 2. Discounted linear exponential quadratic Gaussian control. 2.1. Cost formulation. 2.2. Cost recursions and aggregator functions. 2.3. Infinite horizon costs. 2.4. Arbitrary time-invariant linear control laws. 2.5. Solution to the infinite horizon discounted problem. 2.6. Summary -- 3. Robust permanent income and pricing / Thomas D. Tallarini -- 4. A quartet of semigroups for model specification, robustness, prices of risk, and model detection / Evan W. Anderson -- 5. Robust control and model uncertainty. 5.1. Introduction. 5.2. A benchmark resource allocation problem. 5.3. Model misspecification. 5.4. Two robust control problems. 5.5. Recursivity of the multiplier formulation. 5.6. Two preference orderings. 5.7. Recursivity of the preference orderings. 5.8. Concluding remarks -- 6. Robust control and model misspecification / Gauhar A. Turmuhambetova and Noah Williams -- 7. Doubts or variability? / Francisco Barillas -- 8. Robust estimation and control without commitment. 8.1. Introduction. 8.2. A control problem without model uncertainty. 8.3. Using Martingales to represent model misspecifications. 8.4. Two pairs of operators. 8.5. Control problems with model uncertainty. 8.6. The [symbol] = [symbol] case. 8.7. Implied worst case model of signal distortion. 8.8. A recursive multiple priors model. 8.9. Risk sensitivity and compound lotteries. 8.10. Another example. 8.11. Concluding remarks -- 9. Fragile beliefs and the price of uncertainty. 9.1. Introduction. 9.2. Stochastic discounting and risks. 9.3. Three information structures. 9.4. Risk prices. 9.5. A full-information perspective on agents' learning. 9.6. Price effects of concerns about robustness. 9.7. Illustrating the mechanism. 9.8. Concluding remarks -- 10. Beliefs, doubts and learning: Valuing macroeconomic risk / Lars Peter Hansen -- 11. Three types of ambiguity. 11.1. Illustrative model. 11.2. No concern about robustness. 11.3. Representing probability distortions. 11.4. The first type of ambiguity. 11.5. Heterogeneous beliefs without robustness. 11.6. The second type of ambiguity. 11.7. The third type of ambiguity. 11.8. Comparisons. 11.9. Numerical example. 11.10. Concluding remarks.
