The "Certificate of Authenticity" that comes with the purchase of a US Mint Proof Set is just a piece of paper, and does not impact the value of each of the coins in the set. Proof coins, just as Mint State coins, have a worth or value that is based upon the "grade" or condition of each coin. A perfect proof coin is graded PF70 or PR70. Not all proof coins in a set are the same grade, and not all of them will be perfect, but they are all Authentic. A Mint State coin is perfect if graded MS70. Brilliant Uncirculated coins have grades between MS60 and MS70, Below that coins are considered "circulated" if they are Mint State coins. It takes years of training to professionally grade a coin, and there are four primary companies that strictly follow the grading rules set out by the American Numismatic Association (ANA), one company of which is called National Guaranty Corporation or NGC, the others are PCGS, ICG and ANACS. They are independent companies that certifiy and grade coins for a fee. Independent, because they have no financial interest in the outcome of the grade decided upon, usually by 3 professional graders. I have written an article entitled "The Grade of a Coin Is Everything" which you can read at: http://www.theperfect-coin.com/coin_articles_4.html Once you know the grade of a coin, you can look up the value or worth in a coin price guide such as: www.pcgs.com/prices A proof set can be sent in to one of these coins to be certified and graded. Or, you may just want a single coin from the set certified and graded, as it may only be worth while to have a single coin certified and graded due to the expense. - Robert L Taylor, JD www.perfectdollarcoins.com www.theperfect-coin.com