I'm an American expat, 15 years in the EU, and 10 years working cross-border within the EU. The IRS is very clear that you have to file with them regardless, t

I'm an American expat, 15 years in the EU, and 10 years working cross-border within the EU. The IRS is very clear that you have to file with them regardless, though you may not have to pay anything (due to FEIE or similar). What you haven't mentioned is your legal status in "Spain." Are you on a tourist visa, or do you have legal residency? Do you have a work permit? If you are in Spain under a tourist visa, then you cannot legally be employed in Spain, which means you have no tax duty in Spain. If you happen to be employed by some US company and you happen to be doing work for them while you happen to be sitting in a cafe in Barcelona, well, you are in a legal grey zone-- you do not have the right to work in Spain. You cannot "come clean" with the Spanish government, as you have no right to work there without the proper residency permit. The best you can hope for is they ignore it, the worst is they prosecute you for visa violations. European health systems are tied to legal residency, which can (but does not always) include some duty to pay taxes. If you have a Spanish residency permit, then you have rights to Spanish health care. If you also have a Spanish work permit, the next question is if your employer is registered as a Spanish employer (most US startups are not). If not, again there are problems which make it difficult for you to pay income taxes in Spain. Note that I'm only talking income from your employer. Interest/dividends/capital gains are a whole nuther thing. I'm guessing you are on a tourist visa. Enjoy your time, don't stay longer than 90 days, and buy private insurance. Also, if you try to stretch the 90 days by a quick trip to England, this might only work the first time.