PCGS (Professional Coin Grading Service) is one of the two major coin grading companies in the US. Third party grading services serve to standardize the classification of rare coins according to condition, or grade. Uniformity of grading standards is essential to keeping the market in rare coins liquid, and makes it easier for those who are not professional coin dealers to determine the value of their coins.

Coins graded by a company like PCGS are said to be certified. Certified coins are placed in tamper-resistant packaging to both preserve the condition of the coin and to ensure the authenticity of the grade rating being claimed by a seller. PCGS also offers a number of other services to numismatists, including an influential price guide.

The company publishes this price guide on its website. Users can look up the particular type of coin they own to get a quick assessment of its value in comparison to other coins. Differences in price for a particular coin by grade level are set forth in a grid that dramatically illustrates the economic impact of even slight variations in the condition of a coin.

It should be noted that a coin's grade does not depend solely on the effect of handling or wear and tear on the coin after it was issued. Uncirculated coins, also known as mint state coins, vary in quality according to such factors as strike quality (which affects the level of visible detail on the coin), luster, and overall aesthetic appeal. Individuals who wish to have their coins graded by PCGS can visit their website for more information on the company's grading procedures.