Perhaps it's partly nostalgic haze, perhaps it was that I was drinking it when the temperatures made it taste the most wonderful, but anyway I've been craving the kind of lemon juice served in Vietnam. Lemonade doesn't get it done, and Goya's "Lemon Juice" drink in the bottle, while closer, isn't the real thing.

Anyone have any ideas about how it's made, why it's so good (it may, of course, just be that the lemons are that good!) or am I delusional altogether?

I haven't been to Vietnam yet, but from what I know, the "lemon" juice they serve there is actually what we would call a lime. Maybe it's even Kaffir Lime?
My understanding is that Vietnamese lemonade is lime juice, sugar and carbonated water.

From memory lemon and lime juice seem to be interchangeable in Vietnam. Is it a mixture of lemon and lime juice? I agree with you though, its a very refreshing drink.

The lime juice in Vietnam is actually more like Key Lime than Kaffir Lime,

I am also a huge fan. The quality is probably due to the lemons/limes themselves, combined with a simple syrup.

You can also make an excellent lime/soda drink with the original Rose's lime juice--the natural one, which is hard/impossible to find in the US. (I am assuming you are from the US--correct me if I am wrong) And try looking for Italian lemon sodas in cans--made with real juice and sugar. You might find these in an imported food store.

Thanks, everyone! I'll have to try with the limes, perhaps mixed...I'm guessing a large part was due to the fruit itself. I don't think that my favorite ones were carbonated, just light and delicious. (Actually, this is one of many, many reasons I'd love to be going back to Vietnam, but alas, too many places, too little time!)