What is reinsurance?

Reinsurance is insurance for insurance companies. It is the transfer of some of an insurer's risk to another company, so the insurer can protect its balance sheet, take on larger risks and stay solvent after major loss events such as hurricanes or wildfires.¹

The insurer that buys the cover is the ceding company, or cedant. The company issuing the protection is the reinsurer.² By passing on part of its liabilities, the cedant reduces its exposure and strengthens its financial position, which is why the practice is often described simply as insurance for insurers.¹

The reinsurance definition is straightforward. It is a form of insurance bought by insurers rather than by households or businesses, which is why it is sometimes searched as reinsurance insurance. To reinsure means to pass part of an underwritten risk to a reinsurer, so the original exposure is re-insured a second time at a higher level. In short, the reinsurance meaning comes down to insurers sharing the risk they cannot safely carry on their own.

The relationshipWho carries the risk: cedant, reinsurer and retrocedant

The core transaction is between the cedant and the reinsurer.² When a reinsurer accepts risk from a cedant, that business is classified as assumed reinsurance. The chain does not stop there. A reinsurer that wants to reduce its own concentration of exposure can pass part of its assumed risk to another reinsurer.⁴ That process is retrocession, and the company taking on the risk is the retrocedant.³⁵

This tiered structure, running from primary insurer to retrocedant, spreads the largest and most volatile risks across the global financial system.⁶ It matters most for catastrophe cover, where the capacity of the entire market is sometimes needed to absorb a single extreme event. Retrocession is what stops dangerous concentrations of risk building up inside one company.³⁵

The fundamentalsWhy insurers need reinsurance

Reinsurance is now treated less as a cost and more as a financial instrument for meeting strategic goals.⁸ Insurance executives cite capacity expansion and lower income variability alongside traditional risk transfer as their main objectives.⁹

Protecting core capital

The first function is protecting the insurer's capital base against unexpected severity or frequency of losses.³ By ceding liabilities, the cedant safeguards its balance sheet and holds its regulatory solvency margins, so a high-impact event does not wipe out reserves or threaten its ability to pay policyholders.²

Capital efficiency and balance sheet relief

The strategic value of risk transfer is tied to capital efficiency under frameworks such as Solvency II in Europe.⁴⁰ Solvency II sets high capital requirements, and reinsurance reduces the buffer a cedant must hold to meet regulatory stress tests, which improves its solvency ratios.³ A World Bank study found that a properly structured financial quota share can offer the best capital relief efficiency when measured against alternative debt instruments.⁴¹ The same logic now shapes planning under IFRS 17.²⁷

By freeing capital tied up in loss reserves, reinsurance releases money the insurer can put to more productive use, whether that is generating investment returns or underwriting new and profitable business.³ The cover is a balance sheet management tool, not simply an expense.⁸

Building capacity

Reinsurance lets a cedant write business it could not prudently retain alone.⁹ Large infrastructure projects, international corporate risks and specialist liability exposures carry potential losses far above what a primary insurer can keep on its own books. Without a reinsurer behind it, the cedant would have to decline that business and limit its growth.¹⁶ The scale of the global market, which reached USD 805 billion of dedicated capital at half-year 2025, supplies the depth that individual carriers cannot reach alone.²³

Reducing volatility

Smoothing annual profit is a goal for financial stakeholders.³ By capping maximum annual losses, particularly through non-proportional structures such as excess of loss, the cedant can forecast earnings more reliably, support investor confidence and pay steadier dividends.⁹

High capacity does not mean cheap cover for every peril. Gallagher Re reported that US demand for catastrophe reinsurance was expected to grow by as much as 15% into 2026, and that demand, set against persistent loss experience, keeps rates elevated in volatile property lines.²³ Cedants therefore have to weigh capital relief against the price of the cover.¹⁶

The structureThe two main types of reinsurance

Contracts split into two structural categories, proportional and non-proportional, which set out how premiums and losses are shared.

Proportional reinsurance

Here the reinsurer and cedant share premiums and losses in a fixed, agreed ratio.¹⁷ If the cedant cedes 50% of the risk, the reinsurer takes 50% of the premium and pays 50% of any claim.¹⁹ To cover the cedant's acquisition and overhead costs, the reinsurer pays back a ceding commission.²⁰

The simplest form is the quota share, where a fixed percentage applies across a whole portfolio or class of business.⁹ A surplus treaty works differently. The cedant sets a fixed monetary retained line, and the reinsurer only takes the part of a policy limit that exceeds it, so cession varies with the size of each individual risk.²⁰

Non-proportional reinsurance

With non-proportional cover the reinsurer is triggered purely by the size of the loss the cedant suffers.¹⁰ The most common form is excess of loss. The cedant keeps all losses up to a set attachment point, and the reinsurer pays only the amount above it, up to the policy limit.⁷ This lets the insurer handle everyday claims while transferring the burden of large, unexpected ones.

Catastrophe cover is a specialist form of excess of loss aimed at the many claims that flow from a single severe event such as an earthquake or hurricane.⁷ Its effectiveness depends on how an event is defined. Losses from Hurricane Irma in 2017 caused legal debate because they developed over an unusually long period, tied to specific state insurance laws, which shows that catastrophe cover rests on the legal reading of the policy as much as the physical scale of the disaster.¹⁸

The transactionHow reinsurance is placed: treaty or facultative

The way cover is bought defines the working relationship and the efficiency of the transfer.

Treaty reinsurance is the more common method.²⁴ The cedant agrees to cede, and the reinsurer agrees to cover, an entire portfolio or defined class of business under one contract. It is negotiated once and applies to every eligible policy written during the term, which gives automatic, consistent cover and cuts the administrative load of placing risks one by one.²⁶ The reinsurer underwrites at portfolio level, so individual risks are usually accepted without separate review, and these arrangements tend to signal a longer-term relationship.²⁵

Facultative reinsurance is transactional. It is negotiated separately for a single policy or risk, and it is used when a risk is unusually high-value, complex or hazardous enough to fall outside an existing treaty.² Because each risk is unique, the reinsurer runs its own underwriting review to price the exposure, which gives accuracy at the cost of higher expense for both sides.²⁵ The choice between the two is strategic. Treaty cover suits large-scale capacity across core lines, while facultative cover suits a specific outlier risk that needs individual assessment.²⁴

Market intermediationThe role of the reinsurance broker

The reinsurance broker is the intermediary with the market knowledge and access to structure and place complex cover.²⁶ The work starts with a risk assessment of the cedant's book to set out its requirements, then advice on whether broad treaty cover or specific facultative cover fits best.²⁸ Brokers use their relationships to negotiate terms, secure capacity and give ongoing administrative and claims support through the life of the contract, which keeps them close to the financial health of their cedant clients.²⁶

The marketThe biggest reinsurance companies in the world

Reinsurance is concentrated among a small group of very large carriers. S&P Global Ratings ranked Swiss Re the largest reinsurer in the world in 2025, followed by Munich Re and Hannover Re, with Berkshire Hathaway fourth, Lloyd's of London fifth and SCOR sixth.⁴⁶ Measured purely by gross written premium, Munich Re sits at the top, with more than USD 50 billion written in 2024 according to Statista.⁴⁸

The order shifts with the accounting standard. AM Best splits its table because IFRS 17 changed how many European and Asian reinsurers report, so it ranks Berkshire Hathaway first among non-IFRS 17 reporters at USD 26.9 billion of gross written premium in 2024, ahead of Lloyd's at USD 23.5 billion, with Reinsurance Group of America, Everest and RenaissanceRe close behind. China Re completes the top five among the IFRS 17 filers.⁴⁷ For an insurer or MGA choosing a reinsurance partner, scale is one factor among several, alongside financial strength ratings and appetite for the relevant line of business.

The vocabularyKey reinsurance terms

The market runs on a precise technical vocabulary. These are the terms that carry the contractual mechanics.

The administration of bordereau data is a long-standing weak point. Deloitte found that reporting has not kept pace with the complexity of modern contracts, with many reinsurers still running on legacy systems and manual processes that hold back the analytics needed for sharper risk selection and pricing.²⁵

The outlookWhere the reinsurance market is heading

Reinsurance disperses complex risk across the world, so regional insurers can withstand major low-frequency events without collapsing.¹⁶ The robust pool of global capital keeps cover available and affordable even for the hardest exposures.⁴³

Climate change

Rising frequency and severity of extreme weather is the largest structural pressure on the sector.¹⁸ McKinsey notes that events once treated as low-probability tail risks are happening more often, affecting loss development across the balance sheet.¹⁹ Actual losses have at times run well above modelled expectations, as with the 2011 Thailand floods, and Australia and New Zealand have seen record insured flood losses in recent years.²⁹ Reinsurers have responded with caution and higher property catastrophe rates.²⁶ If rates keep climbing on unchecked climate losses, the risk shifts from reinsurer solvency towards a wider protection gap, the difference between the cover needed and the cover bought.¹⁶

Capital markets and ILS

A structural shift is the growing use of non-traditional capital through insurance-linked securities.²⁰ Catastrophe bonds and collateralised sidecars let reinsurers pass peak risks to institutional investors who want returns uncorrelated with broader markets.²¹ Swiss Re Capital Markets reported the segment growing 10.5% year on year, with outstanding notional projected to pass USD 50 billion. Bermuda has strengthened its regulatory regime to accommodate these structures, and their acceptance points to a lasting change in how catastrophe risk is funded.²²

Market health

Climate pressure and social inflation in casualty lines weigh on the sector, yet the underlying numbers are strong. Global dedicated capital reached USD 805 billion at half-year 2025, and Lloyd's reported an 86.9% combined ratio for 2024.²⁴ Aon argues that the reinsurers who do best from here will pair pure risk transfer with the analytics and advisory insight their cedant clients need, turning data into longer and more profitable partnerships.⁴⁴

As climate losses intensify and risks such as cyber emerge, cedants will keep weighing rising costs against capital efficiency, reinsurers will lean harder on analytics and alternative capital, and brokers will provide more sophisticated advice. Together they keep reinsurance doing its core job: protecting the protectors, so insurers can meet their obligations to policyholders.