Going to Thailand (Bangkok, Chiang Rai and Mai and points in between) and Ankgor Wat January 18-Feb 3. What clothing is recommended? Is anything a no-no? Can we wear shorts? Will long sleeve cotton shirts be needed?

do not take any synthetics, imo..

have all loose fitting garments....all natural fibres...like cotton and linen...shorts are not always good except in resort, imo...you may not feel comfortable in certain places...in religious places in thailand they are not permitted usually...cover your shoulders also...

we do not wear sneakers as we find them too hot....we use sandals and maybe a good walking shoe of leather...

angkor is a bit difficult walking....it is also very hot....

we usually take at least one long sleeve cotton shirt...for sun cover and a/c protection

I am going to BKK in late Sept to early Oct and will be taking my usual capris, t-shirts and loose fitting cotton shirts with sleeves that protect from the sun, a long skirt, and my sandals. BKK is always hot, but Dec to Feb is really the best weather.. a little cooler with nicer evenings.
Carol

Thanks for the help. I have a pretty good idea what women can and cannot wear. What about the men? Are shorts taboo for them also? Can they wear sandals? Where in Bangkok is the best place to buy suitable Thai clothing?

Men are sometimes seen in shorts and sandals, but I think you will see more in khaki pants and shirts.

Re; shopping
If you are petite, you will go crazy buying Thai clothing at places like MBK mall or Pratunam market area. If you are not petite (more typical of Westerners) you will have to go to the more upscale malls to find things that fit you.
Carol

Two items-when you enter Buddhist temples, you must remove your shoes. I always make sure that I am wearing socks. Also, Ex Officio makes wonderful light clothing. The shirts are very cool and dry quicly. Perspiration will drench anything you wear.

Bring enough bras for the whole trip because they do not have a wide variety of sizes. That's something I learned.

The largest size most malls/markets had was size 8, the largest bra size was 34B.