As a dual EU/US citizen planning to move to the EU and establish residency while operating a US-based LLC, your tax situation will involve several considerations at both the federal and state levels in the US, as well as in your new country of residence in the EU. Here are key points to consider:

### U.S. Federal Taxes

1. **Worldwide Income**: As a US citizen, you are taxed on your worldwide income regardless of where you live. This means you must report all income, including income earned from your LLC, on your US tax return.

2. **Foreign Earned Income Exclusion (FEIE)**: If you meet certain criteria, you may qualify for the FEIE, which allows you to exclude up to a certain amount of foreign earned income ($120,000 for 2023, adjusted annually) from your US taxable income. To qualify, you must either:
- Be a bona fide resident of a foreign country or countries for an uninterrupted period that includes an entire tax year.
- Be physically present in a foreign country or countries for at least 330 full days during any 12-month period.

3. **Foreign Tax Credit**: You may be able to claim a credit or deduction for foreign taxes paid on income that is also subject to US tax, which can help reduce double taxation.

### U.S. State Taxes

1. **State Residency**: Whether you need to file state taxes depends on your residency status in the state where you were previously domiciled. If you are no longer a resident and do not have any income sourced from that state, you typically will not need to file state taxes. However, this can vary by state, so it’s important to check the specific rules of your previous state of residence.

### LLC Considerations

1. **LLC Formation**: Forming an LLC in a tax-favorable state like Delaware or Wyoming can offer benefits such as limited liability protection and favorable tax treatment. However, keep in mind that an LLC itself is generally a pass-through entity for tax purposes, meaning the income passes through to the owners (you) and is reported on your personal tax return.

2. **Income Sourcing**: The source of the income (i.e., whether it is considered US or foreign income) can affect your tax obligations. Income earned from services provided outside the US might be considered foreign-source income, which could impact your eligibility for the FEIE or foreign tax credit.

### EU Taxes

1. **Tax Residency**: Once you establish residency in an EU country, you will be subject to that country’s tax laws. Most countries tax residents on their worldwide income, so you will need to report your global income, including income from your US LLC.

2. **Double Taxation Treaties**: Many countries have tax treaties with the US to prevent double taxation. These treaties typically allow you to claim credits for taxes paid to the other country.

### Tax Optimization Strategies

1. **Utilize FEIE and Foreign Tax Credit**: Maximize the use of the FEIE and foreign tax credit to reduce your US tax liability.
2. **Plan Your Travel**: Ensure you meet the physical presence or bona fide residence tests to qualify for the FEIE.
3. **Professional Advice**: Consult with a tax professional who is knowledgeable about both US and international tax laws to optimize your tax strategy and ensure compliance with all applicable tax regulations.

By carefully planning your residency status and utilizing available tax benefits, you can effectively manage your tax obligations as a dual EU/US citizen living abroad.