In our cooking class in Hoi An we learned of the many types of noodles that go into Vietnamese food.

Cau Lao Noodles in the Market in Hoi An.  Cau Lao Pork Noodle Dish, a Hoi An speciality.  A type of Vietnamese rice noodle called Bun. Making rice noodles (bun) for salad rolls and soups.Shrimp noodle soup on our Vietnamese brunch while cruising Halong Bay.Mi Quang noodles. 
Vietnamese noodles for Pho, the famous beef noodle soup.My friend’s Pho soup with ‘beef balls’ and very thin slices of rare beef (and lots of hot sauce!)My Pho soup with Thai basil, bean sprouts and hot sauce added. There are noodles under there somewhere.
More on our December 2013 trip to Vietnam.