The market

What is reinsurance?

Reinsurance is insurance purchased by insurance companies. When an insurer writes a policy — say, homeowner’s insurance in Florida — it takes on the risk that a hurricane could destroy thousands of homes simultaneously. That concentrated exposure can threaten the insurer’s solvency. Reinsurance lets the insurer transfer some of that risk to another company, the reinsurer, in exchange for a share of premium.

The mechanism is straightforward: the insurer (called the cedent) pays a premium to the reinsurer, and the reinsurer agrees to cover some portion of the cedent’s losses under specified conditions. Those conditions are defined in a contract — and as we will see throughout this site, the precise structure of that contract is where all the analytical complexity lives.

Key Insight

Reinsurance is not a different business from insurance — it is the same business operating at a different layer. The fundamental problem is identical: pricing risk and managing capital. The difference is scale, concentration, and the sophistication of the counterparties.

Why reinsurance exists

Insurance works because of the law of large numbers: an insurer pools thousands of independent risks (individual homes, cars, businesses), and the aggregate loss becomes predictable. But some risks are not independent. A single hurricane can damage 100,000 homes on the same day. An earthquake can trigger claims across an entire region simultaneously.

These correlated losses — events that affect many policyholders at once — are called catastrophes. The law of large numbers itself is fine; what a catastrophe violates is the independence assumption that makes pooling effective.¹ When one event drives thousands of claims at once, aggregation stops smoothing the volatility, and that single event can generate losses that exceed the insurer’s capital.

Reinsurance exists to solve this problem. By transferring catastrophe risk to reinsurers, insurers can:

1. Write more business — without reinsurance, an insurer’s capacity is limited to its own capital
2. Stabilize earnings — reinsurance smooths the volatility of catastrophe years
3. Meet regulatory requirements — regulators require insurers to demonstrate they can survive extreme events
4. Access expertise — reinsurers specialize in understanding, pricing, and managing catastrophe risk

The market is a web of interconnected risk transfer, not a simple chain. Multiple policyholders aggregate into a single insurer. Each insurer spreads its risk across multiple reinsurers. Reinsurers in turn buy protection from retrocessionaires — and a retrocessionaire can itself be another reinsurer, standing on both sides of the market (Reinsurer P above). The diagram traces this layered, many-to-many structure.

A brief history

Reinsurance has existed for centuries. Understanding its evolution helps explain why the modern market looks the way it does.

Origins

The earliest known reinsurance contract dates to July 1370, written on a marine cargo voyage from Genoa via Cadiz to Sluys, the port serving Bruges — the reinsurer took the riskier Cadiz-to-Sluys leg.² For several centuries, reinsurance remained informal — ad hoc agreements between merchants sharing risk on specific voyages.

Formalization (19th century)

The Great Fire of Hamburg (1842), which destroyed about a quarter of the inner city, demonstrated that insurers needed systematic risk transfer. It led directly to the first dedicated reinsurance company: Cologne Re, chartered on April 8, 1846, which wrote its first reinsurance treaty in 1852.² Swiss Re followed in 1863, Munich Re in 1880.² Cologne Re proved the model, but Swiss Re and Munich Re became the lasting leaders — both still rank at the top of the industry. Cologne Re’s legacy lives on inside Gen Re, part of Berkshire Hathaway since 1998.³

Catastrophe era (1990s–2000s)

Two events transformed the modern market:

• Hurricane Andrew (1992) — about $15 billion in insured losses at the time,⁴ or $27.3 billion in 2017 dollars.⁵ Published insurer-failure counts differ: the Insurance Information Institute (III) attributes at least 16 insurer failures in 1992–1993 to Andrew,⁵ while an NAIC-published analysis counts 11 direct insolvencies.⁴ Either way, the industry realized its catastrophe models were inadequate and its capital reserves were insufficient.
• September 11, 2001 — about $32.5 billion in insured losses at the time, or $42.9 billion in 2013 dollars.⁶ Demonstrated that catastrophe risk was not limited to natural perils. Triggered a massive hardening of the reinsurance market and a surge of capital into the sector.

These events drove three structural changes:

1. Catastrophe modelling became mandatory — companies could no longer rely on historical loss data alone
2. Capital adequacy requirements were formalized by regulators (Solvency II in Europe, RBC in the US)
3. Alternative capital entered the market through insurance-linked securities (ILS)

The modern market (2010s–present)

Today’s reinsurance market is shaped by several forces:

• Climate change is shifting the frequency and severity of some weather perils — the observed signal is strongest for heat extremes and heavy precipitation, and weaker or mixed for others, such as tropical cyclone frequency⁷; growth in insured losses is also driven by exposure growth, urbanization, and inflation⁸
• Urbanization is concentrating more insured value in catastrophe-prone areas
• Capital markets are playing an increasingly large role through ILS, cat bonds, and sidecars
• Technology is transforming analytics — from spreadsheet-based modelling to real-time portfolio optimization
• Consolidation has reduced the number of major reinsurers while increasing their individual significance

In Practice

The reinsurance market is cyclical. After a major catastrophe, capital exits, prices rise (a “hard market”), and new capital enters attracted by high returns. Over time, competition drives prices down (a “soft market”) until the next major loss. This cycle matters for analytics because the models, risk appetite, and pricing parameters all shift with it.

Where reinsurance operates

Reinsurance is a global business concentrated in a handful of cities.

Major hubs

City	Significance
Zurich	Headquarters of Swiss Re — the largest reinsurer by year-end 2024 reinsurance revenue9
Munich	Headquarters of Munich Re — the second-largest on the same year-end 2024 basis, and the long-time leader on earlier rankings9
London	Lloyd’s of London — the world’s oldest and most specialized insurance/reinsurance marketplace
Bermuda	Tax-efficient domicile for many reinsurers and ILS funds; major hub after 9/11
Singapore	Growing hub for Asian reinsurance business
New York / Hartford	US domestic reinsurance market; Hartford is the historical US insurance capital

Market size

The IAIS reports gross reinsurance premiums of roughly $900 billion by the end of 2023 — a total that spans both life and non-life reinsurance.¹⁰ It is a concentrated market: the ten largest groups together reported about $215 billion of reinsurance business for 2024, the top three about $96 billion.⁹

Rank	Company	2024 Volume	Measure
1	Swiss Re	$36.2B	Reinsurance revenue (IFRS 17)
2	Munich Re	$32.6B	Reinsurance revenue (IFRS 17)
3	Hannover Re	$27.5B	Reinsurance revenue (IFRS 17)
4	Berkshire Hathaway	$26.9B	Gross premiums written
5	Lloyd’s (marketplace)	$23.5B	Gross premiums written
6	SCOR	$16.8B	Reinsurance revenue (IFRS 17)
7	Reinsurance Group of America	$15.6B	Gross premiums written
8	Everest Group	$12.9B	Gross premiums written
9	RenaissanceRe	$11.7B	Gross premiums written
10	Arch Capital	$11.1B	Gross premiums written

Source: AM Best, “World’s 50 Largest Reinsurers,” August 2025, year-end 2024 data.⁹ AM Best ranks IFRS 17 reporters by reinsurance revenue and other reporters by gross premiums written; the two measures are not directly comparable, so read the interleaved ordering as approximate. S&P Global Ratings’ 2025 top-40, ranked on year-end 2024 gross premiums written throughout, also places Swiss Re first, ahead of Munich Re and Hannover Re.¹¹ Lloyd’s is a marketplace, not a single entity.

Beyond the top tier, the market includes dozens of mid-sized and smaller reinsurers. These smaller players — including newer entrants and specialty firms — often concentrate on niches where the large incumbents are less competitive, and some, starting without decades of legacy systems, can move faster on technology. Neither trait is guaranteed by size; it varies company by company. What the mid-tier reliably provides is balance in a market that might otherwise calcify around a few dominant players.

Lines of business

Reinsurance covers many lines of business, but this site focuses on property catastrophe reinsurance — the segment most dependent on sophisticated analytics. Even within property catastrophe, the market distinguishes between sub-segments: residential, commercial, industrial, agricultural, marine, and others — each with different exposure characteristics, data quality, and modelling approaches. Property cat reinsurance covers losses from natural catastrophes (hurricanes, earthquakes, floods, wildfires) and is the segment where:

• Losses are most volatile and extreme
• Catastrophe models are most critical
• Financial modelling is most complex
• The analytical challenge is highest

Watch Out

“Reinsurance” does not mean only catastrophe risk. Reinsurers also write casualty, specialty, life, and health business. However, property catastrophe reinsurance is where the analytical complexity — and the content of this site — is concentrated. When we say “reinsurance analytics” throughout, we mean property catastrophe analytics unless stated otherwise.

How the market is evolving

Several trends are reshaping reinsurance in ways that directly affect the analytics systems that are built:

Convergence of traditional and alternative capital

The boundary between traditional reinsurance and capital markets is blurring. Capital market instruments such as catastrophe bonds and insurance-linked securities, along with collateralized reinsurance vehicles, now supply about 17% of global reinsurance capital: Aon estimates $136 billion of alternative (third-party) capital against $785 billion of total reinsurer capital at year-end 2025.¹² Note the denominator — that is a share of the industry’s capital base, not of the coverage limit it sells. This means analytics systems must handle both traditional contract structures and these alternative capital forms.

Real-time analytics

Historically, portfolio analysis was a quarterly or annual exercise. The industry is moving toward real-time or near-real-time analytics — the ability to price a new contract and see its marginal impact on the portfolio within minutes, not weeks.

Model proliferation

Companies no longer rely on a single catastrophe model from a single vendor. Multiple models, multiple views of risk, and internal adjustments create a combinatorial explosion of analytical trials. Systems must be designed to handle this complexity without becoming unmaintainable.

Regulatory evolution

Two distinct kinds of regime are raising the analytical bar, and they should not be conflated. Prudential capital frameworks — Solvency II in the EU¹³ and the Swiss Solvency Test (SST) in Switzerland¹⁴ — govern how much capital a (re)insurer must hold to survive a bad year and require it to demonstrate solvency to its supervisor. IFRS 17 is something else: an accounting standard that sets out how insurance contracts are recognized, measured, presented, and disclosed in financial statements.¹⁵ Both demand more rigorous and more frequent computation — regulatory capital, solvency monitoring, and financial reporting each pull on the same analytics — so those systems are moving from “nice to have” to “regulatory requirement.”

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The market exists. It is large, concentrated, and analytically demanding. But who are the participants, and how do they interact? That is the subject of the next section.

Footnotes

1. Paul Embrechts, Alexander McNeil, and Daniel Straumann, “Correlation and Dependence in Risk Management: Properties and Pitfalls”, ETH Zürich, 1999 — “insurance has traditionally been built on the assumption of independence and the law of large numbers has governed the determination of premiums.” ↩

2. David M. Holland, “A Brief History of Reinsurance”, Reinsurance News, Issue 65, Society of Actuaries, February 2009. Invitations to found a reinsurer in Cologne went out in December 1842, statutes were drafted in 1843, Cologne Re was founded on April 8, 1846, and its first treaty was written in 1852. ↩ ↩² ↩³

3. Gen Re, “About Us” — Cologne Re (1846) and General Re (1921, acquired by Berkshire Hathaway in 1998) have marketed globally as Gen Re since 2003. ↩

4. Jack E. Nicholson, Karen Clark, and Glen Daraskevich, “The Florida Insurance Market: An Analysis of Vulnerabilities to Future Hurricane Losses”, Journal of Insurance Regulation, Vol. 37, No. 3, NAIC — Andrew “caused $15 billion in insured losses and resulted in 11 insurer insolvencies.” ↩ ↩²

5. Insurance Information Institute, “Hurricane Andrew Fact Sheet” — insured losses of $27.3 billion in 2017 dollars; “at least 16 insurer failures in 1992 and 1993.” ↩ ↩²

6. Insurance Information Institute, “Terrorism and Insurance: 13 Years After 9/11 the Threat of Terrorist Attack Remains Real”, September 2014 — “insured losses of about $32.5 billion, or $42.9 billion in 2013 dollars.” ↩

7. IPCC, AR6 Working Group I, Chapter 11: “Weather and Climate Extreme Events in a Changing Climate”, 2021 — increases in heat extremes are virtually certain and increases in heavy precipitation likely over most land regions, while trends in other extremes, such as tropical cyclone frequency, carry lower confidence. ↩

8. Swiss Re Institute, “Hurricanes and earthquakes could lead to global insured losses of USD 300 billion in a peak year”, press release, April 29, 2025 — underlying risk has grown with “economic and population growth as well as urban sprawl”; a repeat of Hurricane Andrew’s 1992 track today would cost roughly three times as much. ↩

9. AM Best, “World’s 50 Largest Reinsurers”, Market Segment Report, August 18, 2025 — year-end 2024 rankings (Exhibit 1). ↩ ↩² ↩³ ↩⁴

10. International Association of Insurance Supervisors, Global Insurance Market Report 2024, December 2024 — “reported gross reinsurance premiums reaching $900 billion by the end of 2023.” ↩

11. S&P Global Ratings’ 2025 top-40 global reinsurers ranking, based on year-end 2024 gross premiums written, as reported in “Swiss Re, Munich Re and Hannover Re Top List of 40 Largest Reinsurers in 2025: S&P”, Insurance Journal, September 9, 2025. ↩

12. Aon, Reinsurance Market Dynamics, April 2026 — global reinsurer capital of $785 billion and third-party capital of $136 billion at December 31, 2025. ↩

13. European Commission, “Solvency II Overview — Frequently Asked Questions”, MEMO/15/3120, January 2015. ↩

14. FINMA, “Swiss Solvency Test (SST)”. ↩

15. IFRS Foundation, “IFRS 17 Insurance Contracts” — effective for annual reporting periods beginning on or after January 1, 2023. ↩