Mint-made errors are errors in a coin made by the mint during the minting process. Mint error coins can be the result of deterioration of the minting equipment, accidents or malfunctions during the minting process, or intentional interventions by mint personnel. Accidental error coins are perhaps the most numerous and in modern minting are usually very rare, making them valuable to numismatists. Intentional intervention by mint personnel does not necessarily include a deliberate attempt to create an error, but usually involves an action intended to improve quality that miscarries and creates error coins instead. Errors can occur during three different stages of the coining process: the preparing of the planchets, the preparing of the dies, and the striking of the coin. Authentic error coins must not be confused with coins that have incurred damage after being minted, known as post mint damage (PMD) or post strike damage (PSD).

To prepare planchets on which to strike coins, a mint first purchases strips of metal of the correct composition of the coin to be produced. These strips are fed through a blanking machine that cuts them into the metal disks on which the coins are struck, which are known as blanks or planchets. The shape of the coin, whether it be circular, rectangular, or any other shape, is determined by the manner in which the blanking machine shapes the planchets. At this stage, the blanks are type 1 blanks. Next, these type 1 blanks go into an upending mill, which gives the blanks an upended rim, which is where the rim becomes slightly raised and rounds off to the center of the planchet. Planchets with upended rims are called type 2 planchets.