The basic palate of Vietnamese food is salty, sweet, spicy and sour; most recipes involve a specific balance between those 4 things and some of their most basic sauces, such as nuoc cham are clearly made from things designed to give you those 4 flavor elements. (In the case of nuoc cham, salty from nuoc mam, sweet from sugar, spicy from chile and sour from lime and/or vinegar. You'll find very little that's bitter in Vietnamese cuisine.

It's very closely related to Thai food, Khmer (Cambodian) food, Laotian food, Burmese (Myanmar) food and Yunnanese food. These countries are all on or near the Mekong river, which is a source of food and a road system in one. Vietnamese food doesn't have any of the curry or nearly the same level of spiciness that Thai food has, and there's also a bit of a French influence.

Food from northern Vietnam tends to be a bit spicier and a bit simpler than food from the south end of Vietnam. The more complicated and varied foods of southern Vietnam is probably directly related to where the Mekong delta is and where the better ports are; southern Vietnam was the richer half of the country.

Many Vietnamese Buddhists either fast (eat no meat) for one month out of the year or every fifteen days, on the new moon and the full moon. This custom has been around for a long time, so there is a long vegetarian tradition and a wide selection of vegetarian foods.