In Italy, pizza toppings are not exactly limited, but there are a few rules. For example, only meats made with pork are acceptable on an authentic Italian pizza. Salami, prosciutto, ham, sausage – all are pork. Chicken and beef are not used. Beef is rarely seen on top of pizza. Even bresaola, a thin sliced (sliced paper thin, like proscuitto) is hard to find on a pizza.
As far as vegetables and cheeses go, there seemingly is no limit to what Italians might find appetizing on top of their pizzas.
Common Meats - Sausages and Salumi