How do markets spread risk when events are unknown or unknowable and where not anticipated in an insurance contract? While the policyholder can 'hold up' the insurer for extra contractual payments, the continuing gains from trade on a single contract are often too small to yield useful coverage....

Insurance contracts are often complex and difficult to verify outside the insurance relation. We show that standard one-period insurance policies with an upper limit and a deductible are the optimal incentive-compatible contracts in a competitive market with repeated interaction. Optimal group...