Vietnamese food is one of the main reasons people come, and it is easier to eat well here than almost anywhere. The difficulty is not quality, it is navigation: the country's regions cook differently, the best food is often sold by places that make one dish, and the menus are not written for you.
The three regions
The single most useful thing to understand. The north — Hanoi and the Red River delta — cooks with restraint: less sugar, less chilli, more black pepper and herbs, clear broths. This is where pho and bun cha come from.
The centre — Hue, Hoi An, Da Nang — is the spiciest and the most elaborate, with a court cuisine tradition behind it and a fondness for small, complicated dishes. Bun bo Hue, the little steamed cakes, cao lau.
The south — Ho Chi Minh City and the Mekong — is sweeter, uses coconut milk and more sugar, and has the greatest abundance of fresh herbs and produce. Southern pho is sweeter and comes with a plate of herbs that a northerner would find excessive.
How a meal is built
Most Vietnamese dishes are assembled by the eater rather than served finished. A bowl of noodles arrives with a plate of herbs, bean sprouts, lime and chilli beside it, and you add what you want. Grilled meat comes with rice paper, lettuce and herbs to wrap it in.
That is not a garnish you can skip. The herbs are a structural part of the dish, and a bowl eaten without them is a different and lesser thing.
The dipping sauce
Nuoc cham — fish sauce thinned with water, lime, sugar, garlic and chilli — is the thread running through the whole cuisine. Almost everything is dipped in it or dressed with it. The balance varies by region and by cook, and it is worth paying attention to how different it tastes in different places.
The dishes to know
Noodle soups: pho, the beef or chicken noodle soup; bun bo Hue, spicier and with lemongrass; hu tieu, the southern pork noodle soup with a clearer, sweeter broth; mi quang, the central turmeric noodle dish with almost no broth.
Rice dishes: com tam, broken rice with grilled pork chop, egg and pickles; com ga, chicken rice; com binh dan, the point-and-choose canteen rice with several dishes on one plate, which is how most Vietnamese people eat lunch.
Rolled and wrapped: goi cuon, the fresh summer roll; nem ran or cha gio, the fried spring roll; banh cuon, steamed rice sheets rolled around pork and mushroom.
Grilled: bun cha, grilled pork with noodles and dipping broth; nem nuong, pork sausage skewers; banh xeo, the crisp folded pancake you cut and wrap.
The sandwich: banh mi, which needs no introduction and varies enormously from cart to cart.
The things people find difficult
Three honest warnings. Fish sauce is in almost everything and its smell is stronger than its taste in a finished dish — most people who think they dislike it are reacting to the bottle rather than the food. Offal and less familiar cuts appear widely, particularly in noodle soups, and are usually listed, so ask if it matters. And coriander is everywhere; if you are one of the people for whom it tastes of soap, learn to say "khong rau mui".
Chilli is almost always served on the side rather than cooked in, outside the centre. You control the heat.