Chubb Limited, incorporated in Zurich, Switzerland, is the parent company of the Chubb, a global provider of insurance products covering property and casualty, accident and health, reinsurance, and life insurance. ACE operates in 54 countries and territories and in the Lloyd's insurance market in London. Clients of Chubb consist of multinational corporations and local businesses, individuals, and insurers seeking reinsurance coverage.

In 2014, the group had $98.2 billion in assets, $23.4 billion of gross written premiums and approximately 21,000 employees. ACE trades on the NYSE and is a component of the S&P 500 index. Its core operating insurance companies are rated "AA" (Very Strong) for financial strength by Standard & Poor's and "A++" (Superior) by A. M. Best with stable outlooks from both agencies. Fitch rates ACE Limited and its subsidiaries "AA" (Very Strong) for financial strength, "AA-" for issuer default and "A+" for senior debt. Moody's rates the U.S. companies "A1" and the unsecured loan notes "A3".

On July 1, 2015, ACE announced that it will acquire Chubb Corporation for $28.3 billion in cash and stock.
ACE has committed that Chubb's current headquarters in Warren, New Jersey, USA, will have a substantial portion of the headquarters function for the combined company's North American Division. Importantly, the combined company will adopt the Chubb name.

ACE provides insurance and reinsurance products and services through several operating units.

ACE USA provides commercial property insurance and casualty (P&C), risk management and accident and health (A&H) coverages through retail brokers. ACE Agriculture offers crop, farm and agribusiness P&C coverages through agents and brokers. ACE Westchester offers commercial P&C excess and surpluslines through wholesale brokers. ACE Bermuda provides liability, property, political risk coveragesand captive programs through large international brokers. ACE Private Risk Services offers high-value personal lines coverages through independent agents and brokers. ACE Commercial Risk Services provides specialty small business coverages through agents and brokers.

ACE International provides commercial P&C, A&H, and traditional and specialty personal lines through retail brokers, agents and other channels in 51 countries outside North America. ACE Global Markets offers commercial P&C excess and surplus lines and A&H sold by wholesale brokers and through Lloyd’s. In North America, Combined Insurance, acquired by ACE in 2008, provides personal accident and supplemental health insurance through captive agents.

ACE Tempest Re offers P&C and life reinsurance sold worldwide by reinsurance brokers.

ACE Life provides protection and savings products through agents, bancassurance and other channels in Asia, Latin America, and the Middle East. Combined Insurance offers personal accident and supplemental health coverages sold by captive agents in North America.

ACE Limited was established in 1985, funded by a group of 34 U.S. companies seeking difficult-to-obtain Excess Liability and Directors and Officers (D&O) insurance coverage. That year, ACE and its Bermuda subsidiary, incorporated in the Cayman Islands and headquartered in Hamilton, Bermuda, wrote its first insurance policy with John Cox as its President and CEO. In 1987 the company assumed management of Corporate Officers & Directors Assurance Limited (CODA), expanding ACE Bermuda's product line.

Walter Scott became Chairman, President, and CEO of ACE in 1990 and saw the company listed on the New York Stock Exchange in 1993. Brian Duperreault succeeded Scott in 1994 as Chairman, President & CEO and worked for the next ten years as ACE went through a series of acquisitions and a diversification process that brought the ACE Group of Companies global status. One of the multiple acquisitions made during this time was the global property and casualty business of Cigna Corporation (most significantly the Insurance Company of North America, known as INA), which was purchased for $3.45 billion in 1999.

In 2004 Evan G. Greenberg became President and CEO of ACE Ltd. In 2004 ACE was also investigated by NY Attorney General Eliot Spitzer for participating in a bid rigging and price fixing scheme with insurance broker Marsh & McLennan.

In 2008, ACE purchased the accident and health insurance provider Combined Insurance Company of America (founded by W. Clement Stone in 1919) from Aon Corporation for $2.56 billion and the high-net-worth personal lines business of the Atlantic Companies.

Also in 2008, ACE relocated from the Cayman Islands to Zurich, Switzerland. Evan Greenberg described the move as a "natural progression" that would provide ACE with a "better strategic flexibility…and a solid legal and regulatory environment…" The re-domestication was completed in July that year.

In 2010 the ACE company ESIS Inc. was hired by BP to process claims made by the victims of the Deepwater Horizon oil spill.

In 2010, ACE Limited purchased Rain and Hail, LLC for $1.1 billion. Rain and Hail Insurance Service, headquartered in Johnston, Iowa, is an industry leader in crop insurance in the United States.

In 2010, ACE Limited acquired the Hong Kong and Korea life insurance operations of New York Life.

In 2011, ACE Limited purchased agribusiness insurer Penn Millers.

During 2012, they purchased Indonesian insurer Asuransi Jaya Proteksi.

During 2013, they purchased Mexican Surety Lines Company Fianzas Monterrey and Mexican Personal Lines Insurer ABA Seguros.

In April 2014, ACE Limited acquired a majority stake in Siam Commercial Samaggi Insurance PCL from Siam Commercial Bank. Following a subsequent tender offer in June 2014, ACE and its local partner owned 93.03% of the Samaggi.

In October 2014, ACE Limited acquired the large commercial property and casualty business of Itaú Unibanco Holding SA. The transaction made ACE the largest property and casualty insurer in Brazil.

In April 2015, ACE Limited acquired the Fireman’s Fund high net worth personal lines insurance business in the U.S. from Allianz for $365 million. ACE Private Risk Services is one of the largest high net worth insurers in the U.S.

In July 1, 2015, ACE announced that it will acquire Chubb Corporation for $28.3 billion in cash and ACE stock. Upon completion, ACE shareholders will hold 70% while Chubb shareholders will get 30% of the new combined company. The new company will be based in Zurich, Switzerland where ACE Limited's headquarters are located. Evan Greenberg of ACE will be the new Chairman and CEO of the new company, while Chubb Chairman and CEO John Finnegan will be Executive Vice Chairman for North America External Affairs. The company's board will be expanded to 18 with 4 of them coming from Chubb. The new combined company will adopt the Chubb name. It is expected that the deal will close in Q1 2016, subject to approval by ACE and Chubb shareholders, and regulatory approvals.

In 2004 New York Attorney General Eliot Spitzer conducted an investigation in the insurance industry. ACE, American International Group (AIG), Marsh & McLennan, and other large insurers and brokerages were named in Spitzer's investigation for possibly participating in questionable insurance practices including the payment of contingent commissions, bid-rigging, price-fixing, and improper accounting.

Spitzer asserted that contingent commissions contributed to a widespread practice of "bid-rigging" where brokers solicited fake bids with deliberately less favorable terms for the consumer than the bid offered by the insurance company paying the highest commissions.

As part of an $80 million settlement that abated further inquiry, ACE signed an Assurance of Discontinuance in which they acknowledged their prior conduct and agreed to alter their business practices. Evan Greenberg himself admitted no fault in Spitzer's allegations although a junior executive did plead guilty to criminal charges.

Spitzer's insurance industry probe additionally looked in early 2005 into ACE Ltd's subsidiary ACE Tempest Re's reporting to the SEC of a series of reinsurance transactions, together with the SEC reporting of a further 16 unaffiliated reinsurers. Evan Greenberg said that his company's investigation should be completed within a month. According to Greenberg, contracts appeared "generally structured in a way to provide for appropriate risk transfer and accounted for properly."

The Spitzer investigations also triggered civil litigation by policyholders who claim they were victimized by the bid rigging and commission schemes.

On March 9, 2016, George B. Daniels issued a default judgment against Iran, ordering it to pay $7.5 billion in damages to families of victims who died in the September 11, 2001 attacks, as well as $3 billion to Chubb Limited & other unnamed insurers that paid out claims resulting from the event. The plaintiffs in the case argued that Iran "provided material support" and training to al-Qaeda members, including 9/11 hijackers, through Hezbollah prior to the attacks and was therefore liable.