Mezcal is made from over 30 agave species, varieties, and subvarieties, in contrast with tequila, which is made only with blue agave. Of many agave species that can be used to make mezcal, seven are particularly notable. There is no exhaustive list, as the regulations allow any agaves, provided that they are not used as the primary material in other governmental Denominations of Origin. However, the interpretation of this regulation to mean that mezcal cannot be made from blue agave may be a mistranslation. The term silvestre "wild" is sometimes found, but simply means that the agaves are wild (foraged, not cultivated); it is not a separate variety.
Are tequila and mezcal basically the same thing?
Tequila and mezcal are similar in some ways, but they also have one distinct difference. Both liquors are made from agave. Tequila, however, is restricted to using only blue agave in its production process. Technically tequila is a type of mezcal because mezcal encompasses all liquors made from any type of agave. But unless blue agave is used to produce the liquor, it is not tequila.