Vietnamese food is nothing without the imprint of fish sauce (nuoc mam). The best Vietnamese fish sauce is delicately flavored and full of umami goodness. Believe it or not, good fish sauce can be enjoyed straight. Seriously.
You can make fish sauce from various kind of aquatic animals (shrimp, mackerel, or squid, for example). However, the best Vietnamese fish sauce comes from Phu Quoc island, where the waters are full of a particular kind of anchovy called ca com. I was there in 2007 and visited a number of the fish sauce factories.
At first, I didn’t think that Phu Quoc fish sauce could be great. But I was wrong. I visited the source, spoke to the artisanal producers, and then tasted it. Yowza, it was good.
It’s hard to get nuoc mam from Phu Quoc abroad, though the Viet Huong (3 Crabs) brand combines Phu Quoc fish sauce with Thai fish sauce. Viet Huong has a whole line of fish sauce that you should check out.