In the Philippines, the dissolution of a marriage or the legal separation of spouses is governed primarily by Executive Order No. 209, also known as the Family Code of the Philippines. Because absolute divorce is not available under the general law (except for Muslim Filipinos under the Code of Muslim Personal Laws), parties must seek either a Declaration of Absolute Nullity, an Annulment, or Legal Separation.

I. Distinguishing the Three Legal Remedies

It is essential to understand the distinction between these three actions, as they have different grounds and legal consequences.

Declaration of Absolute Nullity (Void Marriages): This applies to marriages that are void from the beginning (void ab initio). In the eyes of the law, the marriage never existed.
Annulment (Voidable Marriages): This applies to marriages that are considered valid until they are set aside by a court decree. The grounds for annulment must exist at the time of the celebration of the marriage.
Legal Separation: This is a "bed and board" separation. It allows the spouses to live separately and dissolve their conjugal property, but the marriage bond remains intact. Neither party can remarry.

II. Grounds for Filing

1. Declaration of Nullity (Articles 35, 36, 37, 38)

Psychological Incapacity (Article 36): The most common ground, where one or both parties are mentally or psychologically unable to comply with essential marital obligations. This incapacity must be characterized by gravity, juridical antecedence, and incurability.
Lack of Requisites: Absence of a valid marriage license or a marriage performed by an unauthorized solemnizing officer.
Incestuous Marriages: Marriages between ascendants/descendants or siblings.
Public Policy: Marriages between first cousins, step-parents/step-children, or those involving the killing of a spouse to marry another.
Bigamous/Polygamous Marriages: Marriages contracted while a prior valid marriage is still subsisting.

2. Annulment (Article 45)

Lack of Parental Consent: If a party was between 18 and 21 and married without parental consent, unless they freely cohabited after reaching 21.
Insanity: Either party was of unsound mind at the time of the marriage.
Fraud: Non-disclosure of a prior conviction, drug addiction, habitual alcoholism, homosexuality, or pregnancy by another man at the time of marriage.
Force, Intimidation, or Undue Influence: Consent was obtained through threats or violence.
Physical Incapacity: Impotence that is permanent and incurable.
Serious STI: One party has a serious, incurable sexually transmissible disease.

3. Legal Separation (Article 55)

Repeated physical violence or grossly abusive conduct.
Attempt of respondent to corrupt the petitioner or a child into prostitution.
Final judgment sentencing the respondent to more than six years of imprisonment.
Drug addiction or habitual alcoholism.
Sexual infidelity or perversion.
Abandonment without justifiable cause for more than one year.

III. Essential Documentary Requirements

To initiate the petition, the following documents are typically required by the Regional Trial Court (RTC):

PSA Marriage Certificate: An official copy from the Philippine Statistics Authority.
PSA Birth Certificates: For the petitioner, respondent, and all common children.
Psychological Evaluation Report: In cases of Psychological Incapacity (Art. 36), a comprehensive report from a clinical psychologist or psychiatrist is vital.
Barangay Certificate: Proving that the petitioner has been a resident of the city or municipality for at least six months prior to filing.
Affidavits: Sworn statements from the petitioner and at least two witnesses.
List of Assets and Liabilities: If there is property involved (titles, registrations, bank statements) for the dissolution of the property regime.

IV. The Judicial Process

The process is rigorous and can take several years to complete.

Filing of the Petition: Filed in the RTC of the province or city where either the petitioner or respondent has resided for at least six months.
Summons and Answer: The court notifies the respondent, who has 15 to 30 days to file an "Answer."
Collusion Investigation: The Public Prosecutor (Fiscal) is mandated to conduct an investigation to ensure the parties are not "colluding" (agreeing) to obtain the annulment/separation falsely.
Pre-Trial: A mandatory conference where the court attempts to simplify issues. In Legal Separation, the law mandates a six-month cooling-off period after filing before the trial can start.
Trial: Presentation of witnesses and expert testimony (psychologists).
Judgment: The court issues a Decision. If granted, a Decree of Annulment/Nullity/Separation is issued.
Registration: The decree must be registered with the Local Civil Registrar (LCR) and the PSA to reflect the change in civil status.

V. Effects of the Decree

Civil Status: For Annulment/Nullity, parties return to "Single" status. For Legal Separation, parties remain "Married" but are legally permitted to live apart.
Custody and Support: The court determines custody based on the "Best Interest of the Child" rule. Generally, children under seven years old remain with the mother. Support obligations are also established.
Property Relations: The absolute community or conjugal partnership is dissolved and liquidated. In Legal Separation, the "offending spouse" may lose their right to a share of the profits.
Succession: In Legal Separation, the offending spouse is disqualified from inheriting from the innocent spouse by intestate succession.