Over the past two decades, Neapolitan-style pizza — a disc of naturally fermented dough that’s topped with tomato sauce and cheese, and then baked — has gone from trend to popular mainstay on menus in pizzerias and casual restaurants throughout the U.S. And aside from the obvious factors (the simple deliciousness of a margherita pizza), there’s at least one other reason for this: a small but mighty Italian association called Vera Pizza Napoletana (VPN).

Established in 1984, VPN includes members from some of Italy’s oldest pizza-making families, and the organization enacts strict standards over what, exactly, can be called a Neapolitan pizza, requiring its certified pizzas to use specific ingredients, baking temperatures, and equipment. Today, it’s a cultural marketing outfit as much as a resource for pizza makers. While expansion remains at the forefront of VPN’s goals, little has changed in terms of the rules.