"... we characterize Pareto-optimal risk-sharing contracts in a market with multiple policyholders and one representative insurer. With minimal assumptions on the risk measures of the parties involved, we characterize Pareto optimality in terms of the minimization of a sum of the agents' risk positions, and we relate it to both the core and coalitional stability of an associated market game. In the special case of coherent risk measures, the optimal indemnity schedules are further characterized in explicit form, in terms of what can be called "worst-case probability measures". "