In the Philippines, the use of a surname by a married woman is governed primarily by the Civil Code and further clarified by landmark jurisprudence from the Supreme Court. Unlike many jurisdictions where name changes are almost automatic, Philippine law treats the wife’s adoption of her husband’s surname as a right, not an obligation.

1. The Principle of "Option, Not Obligation"

Under Article 370 of the Civil Code, a married woman has three options regarding her name:

Use her maiden first name and surname and add her husband's surname;
Use her maiden first name and her husband's surname;
Use her husband's full name, prefixing a word indicating she is his wife, such as "Mrs."

The Supreme Court (notably in Remo v. Secretary of Foreign Affairs) has affirmed that a married woman is not required to adopt her husband’s surname. She may continue using her maiden name even after marriage.

2. Status During Legal Separation

It is critical to distinguish between Legal Separation and the Annulment/Nullity of marriage.

Legal Separation (Bed and Board): This does not sever the marital bond. The parties remain legally married but are permitted to live apart.
The Rule: Under Article 372 of the Civil Code, when legal separation is granted, the wife shall continue using the name and surname she was using prior to the legal separation.

Key Note: If she was using her husband’s surname during the marriage, she is legally entitled (and generally expected) to keep using it after legal separation, as the marriage still exists.

3. Status After Annulment or Declaration of Nullity

When a marriage is terminated or declared void, the rules change based on the nature of the termination:

A. Declaration of Absolute Nullity (Void Marriages)

If a marriage is declared void ab initio (from the beginning), it is as if the marriage never happened. The woman must revert to her maiden name because there was never a legal basis to use the "husband’s" surname.

B. Annulment (Voidable Marriages)

Under Article 371, the rules depend on who was at fault:

If the wife is the guilty party: She shall resume her maiden name.
If the wife is the innocent party: She may resume her maiden name. However, she may choose to continue using the former husband’s surname unless:

The court decrees otherwise; or
She or her former husband marries again.

4. Status After Divorce (Foreign Divorce)

While absolute divorce is not currently legalized for non-Muslims in the Philippines, the law recognizes foreign divorces obtained by an alien spouse under Article 26 of the Family Code. Once a foreign divorce is judicially recognized in a Philippine court, the woman's status returns to "unmarried." Jurisprudence suggests she may revert to her maiden name or continue using the former husband's name following the rules of annulment, provided there is no court order to the contrary.

5. Practical Implications for Government IDs

The R.A. 8239 (Philippine Passport Act) and various BSP circulars align with the "Option" principle.

Situation	Can she revert to maiden name?	Legal Basis/Requirement
During Marriage	No (if already adopted)	Once a woman opts to use the husband's name in her passport, she cannot revert to her maiden name until the marriage is dissolved.
Post-Legal Separation	No	Article 372 requires her to maintain the name used prior to separation.
Post-Annulment	Yes	Court Decree of Annulment/Nullity.
Widowhood	Yes	Death Certificate of the husband.

6. Common Misconceptions

"I am separated (de facto), so I must change my IDs." If the separation is merely factual (living apart without a court decree), the woman's legal name remains whatever she chose at the time of marriage. There is no legal mechanism to "force" a name change due to a mere breakup.
"Using the husband's name is mandatory." As established, the choice belongs to the woman at the start of the marriage. However, once the choice is made and reflected in public records (like a Passport), the government generally requires a legal decree of dissolution to change it back to avoid identity fraud.