Description: Any prudent organization that is obligated to cover health claims will consider the risk that those medical claims vastly exceed expectations. This is true for an employer self-funding employee health benefits, a health system contracted with two-way risk (e.g., Accountable Care Organizations ACOs), and a small or mid-sized health insurance company. Without protection, these risk bearers can incur ruinous losses. Interestingly, the forms of insurance sold to cover such large medical claims, although quite similar, sometimes go by different names depending upon the buyer. • Employer Stop-loss (ESL): self-funded employers who want protection against large unanticipated claims • Provider Excess (PXS): at-risk health systems who have taken delegated risk from a public or private payer and desire protection against large unanticipated claims • Medical Excess/HMO Reinsurance (HMO Re): health insurers (including HMOs) who desire protection against large unanticipated claims The concepts we discuss in this article apply to all three categories of large claim risk.