To regain US citizenship
<p>Say Bob is married to Amy. They are both US citizens. One day, Bob decides to renounce his US citizenship (<em><strong>not for the purpose of avoiding taxes</strong></em>), but his wife remains a US citizen.</p>
<p>In this scenario, is it possible for Bob to get a green card first (by being the spouse of a US citizen) <em><strong>and, eventually, become a US citizen, again</strong></em>?</p>

<p>Yes. There is no legal bar for a previous U.S. citizen from naturalization, assuming all normal conditions for naturalization are followed. There is no specific process for resuming citizenship, unlike in certain other countries (e.g. Canada, Australia and Switzerland).</p>
<p>The <a href="https://www.uscis.gov/laws-and-policy/legislation/immigration-and-nationality-act" rel="nofollow noreferrer">Immigration and Nationality Act</a> is comprehensive on naturalization eligibility and former citizenship is not disqualifying.</p>

<p>Actual renunciation is irrevocable, which means that you can't un-renounce, though an act described in <a href="https://www.law.cornell.edu/uscode/text/8/1481" rel="nofollow noreferrer">8 USC 1481</a> can be challenged administratively challenged with State through a lawsuit: <a href="https://fam.state.gov/fam/07fam/07fam1210.html" rel="nofollow noreferrer">here is the manual</a> on the former option. Taking citizenship in Canada for employment reasons (in the era when certain jobs had citizenship requirements) is not voluntary renunciation, and can be administratively undone. See <a href="https://supreme.justia.com/cases/federal/us/444/252/" rel="nofollow noreferrer">Vance v. Terrazas</a> for the controlling case law on this: what the government has to prove is that the person intended to relinquish the rights and privileges of U.S. citizenship (typically not the case with employment-related other-citizenships).</p>
<p>Assume that he actually renounced citizenship, for a non-tax reason, appearing and signing the correct oath of renunciation before a competent official abroad at a US embassy or consulate. He is now not a citizen: but there is no attainder on his soul, he can apply for admission to the US just like any other non-citizen can. Gaining citizenship by ordinary means is not the same as reversing a renunciation of citizenship.</p>

united-states immigration citizenship green-card