I took Trixie with me from Chicago to Amsterdam last Xmas.
Please check with the country of your destination what you need. For the Netherlands we checked the Embassy's website and it gave us a step-by-step list of what we needed. Fortunately all we needed was some international paperwork that our vet filled out on top of a regular health license required by airlines. Also check with the airlines to see what their requirements are as far as kennels and how far ahead to book the ticket (I flew NWA/KLM and they charged us $250 each way)
Trixie actually did really well. I had put a potty pad in her bag and took her out to the bathroom once every 2-3 hours. Although she really didn't want to go. She actually held it for 14 hours straight (put peed a puddle under the Xmas tree at Amsterdam Airport
)
Do make sure you have nutrical on hand (Trixie was a little freaked out and didn't want to eat on the way, but did lick some nutrical). Also give your yorkie plenty of water (just like people on the plane).
Despite all the worrying ahead of time, it was well worth taking her with us. We probably would have spend at much putting her in a kennel. And it was great having her with us for 2 weeks over the holidays. She had a great time as well!!!
If you have any other questions, let me know!