So, some of you in the motorcycle community will know that crossing borders from Thailand to Laos, Cambodia to Laos etc. can be fairly tricky if you don't know what you're doing. There are a lot of scams people fall for, and fake companies that provide services which are completely unnecessary. Additionally, most of the information you'll find online from other articles, or blogs is completely wrong and people just pay the bribe to get across and tell it like it's the truth. This is all wrong! How do I know? I did it on a Thai motorcycle when everyone told me it was impossible, and in this post, I'm going to share with you exactly how I did it.
Here are the documents you need to take your Thai motorcycle across borders:
Green book (to prove you own the motorcycle)
Valid driving license (and IDP if it is not an ASEAN license)
Valid motorbike insurance
Passport 6 months validity left
First things first I'm going to assume you own your motorcycle and you have the documents necessary to take it out of the country. IF YOU DO NOT, please follow this guide I have created here.
You will need the green book (seen in picture below) to go to any other country outside of Thailand. If you do not have it, and are renting a motorcycle, you cannot take the bike out of the country. You can however ask the rental company if this is something they'll provide, usually it's not as they have 0 guarantee of you ever returning.

If you have this book, you're pretty much halfway there!
Next up, you'll need a valid driving license.
I would recommend having one from your home country, along with an international permit. This is the easiest way to travel with no issues. If, however, you were like me and didn't have a license, obtaining a Thai licence is pretty easy.
I'm not gonna outline how to do that in this article, because I have already written a full piece on the topic here.
Now the benefit of having a Thai license is that, it is an ASEAN license. This means you can (in theory) travel across all ASEAN countries without the need for an IDP or any other supporting documents.
I have done this personally, and in practice from my own experience, I can say this to be true.
If you are on a tourist visa in Thailand, you'll probably only be able to get the 2-year license, which will limit you to ASEAN countries. In theory this license is technically not valid in other ASEAN countries as per the Geneva Agreement, but in practice I have never had any issues in any other ASEAN country.
Once you leave an ASEAN country your Thai license is technically valid in all countries that do not require IDP or CDP for travel (International Driving Permit, Carnet De Passage), as the license is in English.
For more information on countries that require CDP to travel, check here.
Now here's the problem, because you're a tourist, it's likely the only license Thailand will give you is the 2-year temporary license. This supposedly does not allow travel outside of Thailand AT ALL. However, your mileage may vary as there are reports online of people being able to hire cars in England with a 2-year temp license.
If you want to be water tight on everything, you will need to get a 5-year license. This is much harder, and requires you to have already held a 2-year license for 1 year and 1 month, before applying for renewal to a full-fledged 5-year.
On top of this, you'll need a valid visa to even obtain a 5-year license, otherwise Department Land Transport will simply give you another 2-year license.
From what I understand the Digital Nomad Visa, the Elite Visa, and ED Visas only allow you to get the 2-year license as Thailand considers them all tourist visas and not permanent residence visas. So, the only workaround I can currently see is getting a work visa which is an incredible amount of effort (you might as well just get a license at home unless you want to do an English teaching stint).
Phew! Now that's all out of the way, how the hell do you get across the border?
Here is a complete list the Thai-Lao border crossings you can use:
Chong Mek
Mukdahan
Nong Khai
Chiang Khong
Huai Kon
There are a lot of Thai-Lao border crossings, but there is only 1 you can use without having to pay a hefty fee for a service or company that will help you across, and even at that border, they try it on!
Chong Mek is the only border you can physically cross with a 125cc motorcycle and above.
Once you have crossed, you can return at any border, since the paperwork has already been acquired.
For instance, I left at Chong Mek, then returned at Nong Khai. If I was to leave at Nong Khai, I would have to pay a hefty service to move my motorbike across the border. However, returning I had nothing to pay.
So how do you cross at Chong Mek?
The process is actually very easy, do get across the Chong Mek border into Laos with a 125cc, follow these steps:
Drive to Chong Mek
Talk to customs on the Thai side and get a temporary export permit (pictured below)

Talk to customs and say you need to get permission to take your bike to Laos BEFORE stamping out of Thailand, if you don't do this, you could be stuck in no-mans land with nowhere that will accept you back with your motorcycle. Some scammers take advantage of this. BE CAREFUL!
Drive to the Laotian border side and park up
Walk to the customs offices, but do not talk to them just yet, on the very far left, close to customs office 1, there is a small room with 2 machines inside
Walk up to these machines, ignore the man offering "company services" and start the process (he is persistent, just say no I'm going to do it myself)
On the keyboard, click the world sign and change the language to English so you can enter the information.
You will not see an option anywhere for 125cc bikes, it is hidden behind the "custom vehicle" option
Click "custom vehicle" and enter your information here
Fill out the required information, submit and then collect your printed paper
You now have to head to customs office 1 where you will pay 60,000 kip ($2-3 USD).
After you have finished this process, you need to head back to Thailand to stamp out of the country through the normal foot passenger route.
Once you have done this, you need to get a piece of paper from a small office that is located on route to the Laotian border side. Just as you come up from the underpass, there is a small, green office that has a brown-coloured window and the Laotian insignia, go to them, and fill out the form they give you.
After this, get your tourist visa for Laos through the normal foot passenger route. The cost of a visa is roughly $30-$40 USD for 30 days.

Once you have all of the documents and your visa, you can now drive your motorcycle through the main customs area. They will check your documents, stamp some things and you're free to go!
You can also purchase optional insurance for around $12 on the Laotian side. This will cover you for 30 days
If you are struggling with following the steps above, I have a full video that covers the topic here. When you click the link, the video will start at the correct time, so you can watch the border crossing process.

The document above is the temporary export permit for a motorcycle from Thailand. As you can see from the document, it only allows 30-days maximum until the motorcycle must be returned to Thailand.
These are available for tourists and Thai nationals directly from the border. If however, you would like to export your motorcycle for longer, you need to enquire at the Department Land of Transport office where your motorcycle is registered.
They will provide options for a longer export (if needed).
If you go over the 30-day limit on your motorcycle export permit, the charge is as follows: 1,000 baht/day, with a maximum limit of 10,000 baht. This is around a $200-300 USD charge if you choose to stay longer.
However, if you never return the motorcycle to Thailand, you are required to pay the fine stated on your customs export document. As you can see above, this is 255k baht ($7k USD).
I know some riders who never returned, and they don't plan on returning who haven't paid this fine at all. If they went back to Thailand they would most likely have to pay the fine.
That's it! Enjoy your journey into Laos my friends!