Life insurance companies, which sell life insurance, annuities and pensions products.
    Non-life or general insurance companies, which sell other types of insurance.

In most countries, life and non-life insurers are subject to different regulatory regimes and different tax and accounting rules. The main reason for the distinction between the two types of company is that life, annuity, and pension business is very long-term in nature — coverage for life assurance or a pension can cover risks over many decades. By contrast, non-life insurance cover usually covers a shorter period, such as one year.

Insurance companies are generally classified as either mutual or stock companies. This is more of a traditional distinction as true mutual companies are becoming rare. Mutual companies are owned by the policyholders, while stockholders (who may or may not own policies) own stock insurance companies. Other possible forms for an insurance company include reciprocals, in which policyholders 'reciprocate' in sharing risks, and lloyds organizations.

Insurance companies are rated by various agencies such as A.M. Best. The ratings include the company's financial strength, which measures its ability to pay claims. It also rates financial instruments issued by the insurance company, such as bonds, notes, and securitization products.

Reinsurance companies are insurance companies that sell policies to other insurance companies, allowing them to reduce their risks and protect themselves from very large losses. The reinsurance market is dominated by a few very large companies, with huge reserves. A reinsurer may also be a direct writer of insurance risks as well.

Captive insurance companies may be defined as limited-purpose insurance companies established with the specific objective of financing risks emanating from their parent group or groups. This definition can sometimes be extended to include some of the risks of the parent company's customers. In short, it is an in-house self-insurance vehicle. Captives may take the form of a "pure" entity (which is a 100% subsidiary of the self-insured parent company); of a "mutual" captive (which insures the collective risks of members of an industry); and of an "association" captive (which self-insures individual risks of the members of a professional, commercial or industrial association). Captives represent commercial, economic and tax advantages to their sponsors because of the reductions in costs they help create and for the ease of insurance risk management and the flexibility for cash flows they generate. Additionally, they may provide coverage of risks which is neither available nor offered in the traditional insurance market at reasonable prices.

The types of risk that a captive can underwrite for their parents include property damage, public and products liability, professional indemnity, employee benefits, employers liability, motor and medical aid expenses. The captive's exposure to such risks may be limited by the use of reinsurance.

Captives are becoming an increasingly important component of the risk management and risk financing strategy of their parent. This can be understood against the following background:

    heavy and increasing premium costs in almost every line of coverage;
    difficulties in insuring certain types of fortuitous risk;
    differential coverage standards in various parts of the world;
    rating structures which reflect market trends rather than individual loss experience;
    insufficient credit for deductibles and/or loss control efforts.

There are also companies known as 'insurance consultants'. Like a mortgage broker, these companies are paid a fee by the customer to shop around for the best insurance policy amongst many companies .

Similar to an insurance consultant, an 'insurance broker' also shops around for the best insurance policy amongst many companies. However, with insurance brokers, the fee is usually paid in the form of commission from the insurer that is selected rather than directly from the client.

Neither insurance consultants nor insurance brokers are insurance companies and no risks are transferred to them in insurance transactions.

Third party administrators are companies that perform underwriting and sometimes claims handling services for insurance companies. These companies often have special expertise that the insurance companies do not have.

Reference: www.wikipedia.org