Proof quality was developed as a special way of making coins for presentation. The term “proof” is typically used to describe a coin’s condition, but technically it refers to a special class of coin that has been manufactured a certain way. Where regular minted coins may have softer details and slight imperfections, proof coins are virtually flawless with sharp, high-relief detail, an unusually bright surface, and a high “wire rim.” Errors in proof sets tend to be scarcer, because more attention is paid in both the production and inspection of these coins. Proofs are exceptional coins, and generally grade MS65 or higher. 

The manufacturing process of proof coins is extremely precise and detailed. First, dies are carefully inspected and thoroughly polished and cleaned. The dies are wiped clean after every 15 to 25 impressions, and are replaced frequently to avoid any error that would result from overuse. Only specially cleaned planchets are used for these coins in order to assure the highest quality possible. The planchets are placed into the coinage press one at a time. Each coin is double struck at a low speed and high pressure, ensuring each coin gets struck fully. Each finished Proof is inspected thoroughly and handled with extreme care, and then the coin receives one final inspection before it is packed and sealed for distribution. 

There are variations in Proof types. “Frosted Proofs” have been struck with dies polished only in the fields, but with the details of the image intentionally given a dull finish. “Matte Proofs” are a type that have a granular surface and are seen less often, as opposed to a mirror-like finish. “Brilliant Proofs” have a completely uniform, mirror-like surface with sharp detailing.

Proof Sets initiated as “specimen” coins, are minted from polished regular-issue dies and polished blanks. In 1858, individual Proof coins were first made available to collectors from the Philadelphia Mint, but the U.S. stopped striking Proof coins after 1915. Many speculate that it was due to World War I, or because mint authorities believed the already high quality of regular-issue coins made Proofs unnecessary. Production resumed in 1936, and the U.S. Mint began selling both individual coins and Proof Sets. The sets struck in 1942 included a 5-coin and 6-coin version in order to offer collectors the option of obtaining the Silver Wartime Nickel. The striking of Proof coins was again temporarily halted from 1943 until 1949 due to World War II. 

In 1950, President Harry Truman signed a bill reauthorizing Proof Sets. At this point, single Proof coins were no longer available. These Proof Sets lasted until late 1964, when the Treasury discontinued them due to a shortage of normal coins. The mints would be converted to run more efficiently and be used exclusively to produce coins for general circulation. 

To compensate for this discontinuation, the San Francisco Mint struck “Special Mint Sets” (SMS) for numismatists. Though all SMS coins were struck at the San Francisco Mint, none have the ‘'S’ mintmark, since the sets were made only in years when mint marks were omitted from U.S. coins. 

Proof Set production resumed in 1968, and since then, has been struck at the San Francisco Mint. The 1968 coins form the first such “set” from a branch mint. The 1968-S Proofs are the first Proof Set with a mintmark. 

Throughout the years, Proof sets have been offered in several different denominations and styles:

• From 1936 - 1972, they included the Cent, Nickel, Dime, Quarter, and Half Dollar.
• Proof Sets from 1973 - 1981, and 2000 on, include the aforementioned pieces as well   as the Dollar.  
• Proof Sets from 1982 - 1998 reverted back to the Cent, Nickel, Dime, Quarter, and Half Dollar.
• Proof Sets from 1999 - 2009 included five different Statehood Quarters. 1999 Proof Dollar coins (Susan B. Anthony dollars), were sold separately.
• Beginning in 2007, Proof Sets included the four-piece Presidential Dollars.
• Proof Sets in 2009 were the largest ever available, featuring 18 coins:
• Four different reverse designs for the Lincoln Cent (to commemorate the Lincoln bicentennial)
• Six Quarters (commemorating Washington, D.C. and the five U.S. territories)
• Four Presidential Dollars
• The Sacagawea Dollar
• Jefferson Nickel
• Roosevelt Dime
• Kennedy Half Dollar