Olive oil is the fundamental ingredient in Italian pasta dishes. Classic spaghetti aglio e olio consists of just pasta, garlic, chili and quality extra virgin olive oil.
Pesto alla genovese requires good Ligurian olive oil — light and delicate, so it doesn't overpower the basil. Southern Italian pasta dishes use more intense oil.
An important rule: always add a drizzle of raw extra virgin olive oil on finished pasta as a finishing touch. It adds aroma and ties flavors together.