Do I need a work visa if I'm freelancing while traveling?

This is not legal advice. Actual local laws may vary, you will need to inquire for each country.

Generally people do not request a visa for such situations. You will still be employed in the US, where you are allowed to work and be working for that company. So you are not working for a local company and are not being hired by anyone in the country you will be temporarily located in. This happens all the time:

• People go on vacations and squeeze in some work from where they are.
• A company sends someone to meet with clients, providers or collaborate with offices of the same company located in other countries.
• Someone is sent to a conference to represent or attend.

There are all common cases for someone to be outside their country of work while still working. There are countless more variations. I have personally experienced all the ones listed above and never got a work visa for this. A few times, the company provided me and colleagues with a preemptive letter that stated that I am going for work but remain employed and being paid in my country of employment. This letter was to present to immigration, if asked. No official even asked even though on the entry forms it was said that I was travelling for work. Note the wording, it was travelling for work, not to work.

(You will probably get different Answers.)

This is a highly debated topic here and other forums. The three sides usually cluster around these interpretations:

• NO as there is no realistic way for local officials to know what you're doing, especially if you are not employed or compensated in any way by a local organization. People work on their existing job in other countries all the time so that is in no way unusual.
• YES, because you are working and getting paid, regardless of the circumstance and where you're getting paid.
• NO because you're not being paid to be there specifically or you have an existing job and are not affecting the local labor market or you fit into a specific local exemption.

If you solicit any type of local work, even volunteering, you need to check the specific restrictions for that country.

While it's highly unlikely this will ever even come up at a border, you should be truthful and tell them you keep a full-time job in the US.

Any of the countries where you plan to travel/work might decide that you need a work visa, and that you have to pay income tax. The existing rules for business travelers, etc., might not cover your situation. You are not tax exempt just because you work online.

De jure there are dozens of complex laws and regulations regarding remote employment, under which you may or may not need a special visa in order to work remotely in a given country. Tax laws are an additional complication, where countries such as the UK can deem you as a tax resident for spending as little as 16 days on British soil. And things might be even more complicated if your employer has an office in the country of your travel.

De facto, as long as you don't mention your remote job to immigration personnel at the airport, there's a 99.99% chance no one will ever find out. There are millions of people breaking the law by being employed at on-site jobs in any given country, so digital nomads are a pretty low priority for law enforcement.