My wife and I would like to take a trip to southeast Asia next year, which would certainly include Vietnam, Cambodia, and maybe Thailand and Laos as well. What is the best time to go? It looks like tours in the latter part of the year (October - December) sell out the quickest, which may be a clue. \

Vietnam, being so long, can have several seasons going on at once, In the winter months, it can be quite cold. I'm much more familiar with Cambodia, where the monsoons usually end in Sept/early October. Fall will be fairly dry and cool, and the fields will be lush and green. November- February are cooler still, but it is also more brown.
It starts heating up and getting very humid in March. April is when everyone who lives there tries to head for cooler places! December is high season in many parts of all of these countries. I'd choose early november for the best balance of weather and cost.

And by cool in November I mean a few days will hit the mid-eighties with lowered humidity, if you're lucky! You can head for the hills or Northern Vietnam for colder weather

In my opinion, March to April is the best travel time!

"What's the best time of year to take a trip to Vietnam and Cambodia?"
A pretty straightforward question that you would think would be easy to answer - it’s not!. It really depends what you mean by "best" and what you want to see and do. In terms of weather, in Cambodia, Laos and Southern Vietnam, blue skies and reasonable temps are likely from October to March. It will get a lot warmer towards the end of that period. If I had to chose a specific month for that regions, I would probably go for late October/ November. The downside to travel at that time is that it is the high season and hordes of tour groups visit then. In most places this will not really make much of a difference except in slightly raised prices for hotels and even that is mainly applicable to the higher end places. The big difference will be in Siem Reap which is overrun at that time making it, imo, pretty unpleasant in terms of crowds. I have visited several times in different months and much preferred it without the crowds in the wet season (or on the cusp of the wet season) when it is quieter, greener and cheaper.

The north of Vietnam is generally pretty good Nov - April but avoid the central region from Sept- December when heavy storms and occasionally severe flooding are likely.

I find this tour operators site invaluable for choosing when to travel in SEA https://www.selectiveasia.com/vietna...ather/november

I would avoid Laos in March - April when the smoke from burning the forests etc can be awful.

Thank you, https://www.fodors.com/community/profile/lcuy/and https://www.fodors.com/community/profile/crellston/ for your detailed and thoughtful responses, and to https://www.fodors.com/community/profile/dinho/ for your input as well!

The best time to visit Vietnam and other southest asia is Spring (Jan-March) & Autumn (Sept - Nov) which is not so hot. And you may have chance to see cherry blossoms and mountainous flowers (in spring) or colorful step paddy fields before harvesting.