Both are distilled alcoholic drinks from maguey made in Mexico.
But tequila is only from blue agave, and is made in the Mexican state of Jalisco, while mezcal can be from thirty different species of maguey, and is made in several states – but most prominently in the southern state of Oaxaca.
The most essential difference is the maguey used to make mezcal is roasted, lending it the “smoky” essence it is famous for.
An old, old spirit, mezcal is nonetheless newer to the international market. While lots of delicious cocktails have been invented to enjoy it, some aficionados are purists, insisting it must be appreciated alone. When taken by itself, or “neat,” it is meant to be sipped, or “kissed.”