Residence, Taxation, Property & Business in the Principality
The Principality of Monaco is the world's second-smallest sovereign state (after Vatican City) and the most densely populated. Key facts:
Due to a 1963 treaty between France and Monaco, French citizens living in Monaco are subject to French income tax as if they resided in France. This was designed to prevent wealthy French from escaping French taxes by moving 20 km down the coast.
This does NOT apply to Americans—as a US citizen, you're subject to US taxation regardless of where you live, but Monaco itself won't tax your income.