What US citizen needs to do to get Spanish residency ?

Contacting your nearest Spanish Embassy or consulate will get you the answers.

You would need to speak to a Spanish embassy about immigration for a non European. It is most probably exactly the same as Europeans wanting to emigrate to the USA which is difficult. European citizens which includes Britain can live in any European country.

Well if you are not needing/wanting to work, it's a bit easier.  They have a visado non-lucrativo, the requirements are
- Proof of income; approx Eu 2.5k first person (head of household); Approx Eu .55k each additional family member
- Medical insurance.  Mine, for 4 people, is Eu 240/month
- Police clearance.  I don't know where they start the cull; parking ticket, misdeameanor, felony.  I didn't have any of those.
- Medical clearance for contagious diseases
-  Kids under 18 have to go to school and you'll need acceptance into a school.  My oldest son attended a private school (easier to get acceptance from overseas), youngest daughter went to public school (free)
- You can't work under this visa

There's also a "Golden Visa", you buy a property of Eu 500k or more, the proof of income requirement is waived.  Not sure if you can work on this or not.

I know of at least 3 other Americans who live here in Spain under non-lucrativo, and 2 that purchased property.

The US has NO Equivalent to this, that I know of.  Maybe they have a "Golden Visa".  For that matter, neither does the UK

Good luck and regards

Just to disclose, I haven't moved to Spain and haven't gone through the process yet (US to Spain).  But I have done some research.

Contacting the Spanish Consulate (e.g. Chicago, Boston, etc.) closest to your home is a good thing because Spain's website in the US only provides summary information.  But start with "Residing in Spain".

There are multiple long term visas.  Read this article.  The easiest one to obtain is the non-lucrative residence permit.  This is perfect for retirees but you cannot work even remotely.  That includes logging to your office network in the US.  If you want to work, then go for the lucrative one.

BTW, the information is not the same on each consulate.  Compare Chicago to Boston.  Thus, it is best to call the consulate to get the list of documents you need to fill out and submit when you go for your interview.

If you have citizenship from one of Spain's colonies (e.g. Puerto Rico, Philippines, etc.) in addition to your US citizenship, you may want to mention that to the Consular.

I meant to write "Spain's former colonies".  For some reason, the site won't allow me to edit my post.

Of course the first question is when the US will have COVID controlled enough to get you permission to cross the big pond. The visa process itself took us about six months (three month of prep and planning plus another three months once we applied for an appointment). Will that be enough time for sanity to prevail on the pandemic front?

Anyway, you probably already know each Spanish consulate in the US has responsibility for a defined geographical area. For example, because we were legal residents of Washington State when we were applying for our non-lucrative (retirement) visa back in 2018, we had to do everything through the San Francisco consulate.

Each consulate has slightly different standards for what they need and what they will accept, so be sure to check their website for the latest requirements for the one you will use. Requirements change frequently. (I know varying requirements for the same end result seems rather wonky, but get used to it -- it's the way bureaucracy seems to work in Spain!)

For what it may be worth, we found the following posting very helpful in assembling what we needed for our application in San Francisco: https://frugalvagabond.com/get-non-lucr … sa-spain/.

I'll be happy to answer specific questions about our process. We also have friends here who went through the Boston consulate and probably have a few tips to pass along on how it worked there.

One other heads-up: Your residence visa is only good for 90 days, so once you arrive in Spain, there's another paper chase to get your first residencia application in process before the 90 days runs out. We should chat more about those specifics after you've started the visa process. Just be aware the necessary steps are different for US citizens, so be sure you're not following advice meant for the Brits.