Purists tend to think of pizza as an artisanal flatbread that happens to have toppings, while for many aficionados toppings are the stars and the crust is an afterthought. Both camps place the sauce in a secondary position, but your sauce -- and the herbs that flavor it -- can make or break your pizza. Most pizzas employ a relatively small handful of herbs and other seasonings, but their proportions make each pizza different.
The Dominant Herbs
The cornerstones of pizza seasoning consist of basil and oregano, both members of the extended mint family. Basil's sweetly fragrant flavor brings out the sweetness and fruity notes in your tomatoes, while oregano's sharper, peppery pungency complements the spiciness of your toppings. Pizza makers generally rely on the dried versions of the herbs for making sauce, partially for convenience and partially because both retain their flavors admirably when dried. They're most flavorful when heated and softened in a small quantity of butter or oil before you add them to the sauce. Oregano is far stronger than basil, so add it sparingly until you're happy with the balance.
The Secondary Flavors
Pizza cooks add subtlety to those basic flavors by adding smaller quantities of other herbs common to Italian cooking. The woodsy flavor of rosemary, the sharp camphor notes of sage, fennel's gentle hint of licorice and thyme's peppery complexity can all contribute to a well-rounded sauce. Add them in small quantities -- especially sage and rosemary -- and taste frequently, until you arrive at a combination that pleases your palate. These are present in most commercial "Italian seasoning" mixtures, so you might opt to add a pinch of that rather than each herb separately. Then, round out your flavors by adding either fresh or dried garlic and onion, as well as salt, pepper or hot pepper flakes as desired.
While the sauce is typically made with dried herbs, you can also choose to add color or fresher, brighter flavors with a sprinkling of fresh herbs. This is an especially useful technique when you're attempting to spike up a bland prepared sauce, rather than making your own. Whole, torn or minced leaves of fresh basil provide an obvious choice, with basil serving as the green portion of the patriotically tri-colored Margherita pizza. Leaves of arugula or spinach also work well on pizza, lending a vivid color and -- in the case of arugula -- a peppery flavor. Chopped chives or green onions add a mild and pleasant onion flavor.
Herbs play an important role in conventional pizza, but they're front and center on pizza bianca, or "white pizza." For this variant, you skip the heavy tomato sauce, simply brushing the crust with olive oil and then adding herbs and a modest set of toppings. In the absence of tomatoes, pizza bianca can showcase more subtle herb flavors and show the herbs to great aesthetic advantage. Substitute sweet marjoram for its cousin, oregano, for a milder flavor and faint citrus notes. Delicate feathery fronds of fennel add a muted licorice flavor and a beautiful visual, while parsley -- not assertive in its own right -- adds a bold green color and enhances the flavor of other herbs.