Although reinsurance is an unknown aspect of the insurance industry to many, its roots can be traced as far back as the late 14th century, according to the Washington-based Reinsurance Association of America. While the early focus of reinsurance was in the lines of marine and fire insurance, it has expanded during the last century to include virtually every aspect of the modern insurance market.

Global business

Reinsurance is a global business. Its international nature reflects a further spreading of risk and access to broader capital markets to help cover losses, including natural disasters. Reinsurance can be purchased from three distinct sources:

1. 1. Reinsurance companies located in the United States.
   2. Reinsurance departments of U.S. primary insurance companies.
   3. Alien reinsurers that are located outside the U.S. and not licensed here.

$41.5B net premiums written in 2015

Reinsurance is big business. For 2015, a total of 26 global reinsurance organizations reported reinsurance net premiums written of $41.5 billion, premiums earned of $40.3 billion, loss and loss adjustment expenses of $26.5 billion, commission and broker expenses of $7.8 billion, and other underwriting expenses of $3.3 billion, according to the Reinsurance Association of America's 2015 industry results report. About 46% of all U.S. property and casualty reinsurance premiums, and two-thirds of all U.S. property catastrophe reinsurance premiums, are written by foreign reinsurance companies. Related: 5 ways to fund reinsurance beyond premiums Let's take a look at one slice of the reinsurance pie. Above are the top 10 U.S. reinsurers of U.S. business by gross premiums written in 2015, as ranked by the Insurance Information Institute. For more information, see the Reinsurance Association of America report, "Reinsurance Underwriting Review: A Financial Review of U.S. Reinsurance, 2015 Industry Results." Related: Reinsurer cites lesson of failed marriages in shunning M&A Inside Lloyd's: Writing a reinsurance risk at Lloyd's of London How to find $1M or more in your reinsurance contracts