I am the landlord of an unfurnished property. How do I declare my rental income to the tax authorities?

You must report it each year on your income tax return. Rent from unfurnished property is taxed as property income (under the micro-foncier regime if your annual gross income is less than €15,000 per year, or under the actual-expenses regime if it is higher) (Arts. 14 and 32 of the French General Tax Code).