A.M. Best is a credit rating agency that began reviewing insurance companies back in 1899. Issued annually, its grades illustrate an insurer's ability to pay out on claims and meet other financial obligations.CNBC Select often uses A.M. Best's ratings to help determine the best insurance companies in many different categories.Here's what you need to know about A.M. Best ratings, including what they rank, how grades are determined and how you can use them when shopping for insurance.A.M. Best ratingsWhat is A.M. Best?How does A.M. Best rate insurance companies?What is the A.M. Best rating scale?How to use A.M. Best's ratingsBottom lineFind the best auto insuranceWhat is A.M. Best?An insurer has to be financially healthy to be able to pay out claims. As an independent credit rating agency, A.M. Best translates balance sheets and other data into letter grades that can be understood by consumers, investors and others in the insurance industry.A.M. Best reviews and rates over 16,000 insuran...