Many institutional insurance purchasers buy insurance through an insurance broker. Brokers represent the buyer (not the insurance company), and typically counsel the buyer on appropriate coverages, policy limitations. A broker generally holds contracts with many insurers, thereby allowing the broker to "shop" the market for the best rates and coverage possible.

Insurance may also be purchased through an agent. Unlike a broker, who represents the policyholder, an agent represents the insurance company from whom the policyholder buys. An agent can represent more than one company.

Reference: www.wikipedia.org