In the Philippines, where divorce remains legally unavailable (except for specific cases involving Muslims and certain mixed-nationalities), Annulment and Declaration of Nullity of Marriage are the primary legal avenues for dissolving a marital bond. While often used interchangeably in casual conversation, they are distinct legal concepts under the Family Code of the Philippines.

I. Annulment vs. Declaration of Nullity

Before proceeding, it is vital to distinguish between the two:

Annulment (Article 45): Applies to a "voidable" marriage. The marriage is considered valid until the moment it is set aside by a court decree.
Declaration of Absolute Nullity (Article 35 & 36): Applies to a "void" marriage. The marriage is considered to have never existed from the beginning (void ab initio).

II. Grounds for Filing

1. Grounds for Annulment (Voidable Marriages)

A petition for annulment must be filed within a specific prescriptive period (usually within five years of discovery or reaching majority age) based on the following:

Lack of Parental Consent: If either party was between 18 and 21 years old and married without parental consent (unless they continued living together after reaching 21).
Insanity: If either party was of unsound mind at the time of marriage.
Fraud: Obtaining consent through deceptive means (e.g., non-disclosure of a prior conviction, drug addiction, or pregnancy by another man).
Force, Intimidation, or Undue Influence: If consent was obtained through coercion.
Physical Incapacity: Impotence that is permanent and appears incurable.
Serious Sexually Transmitted Disease (STD): If the disease is permanent and appears incurable.

2. Grounds for Nullity (Void Marriages)

These marriages are invalid from the start and the action does not prescribe (it can be filed anytime):

Psychological Incapacity (Article 36): The most common ground used. It refers to a party's inability to comply with the essential marital obligations due to a psychological condition existing at the time of the celebration, even if it only becomes manifest later.
Minority: Either party was under 18 years old.
Lack of Authority: The solemnizing officer had no legal authority.
No Marriage License: Except in specific exempt cases (e.g., marriages in articulo mortis).
Bigamous or Polygamous Marriages.
Mistake in Identity.
Incestuous Marriages (e.g., between siblings or direct ascendants/descendants).

III. Basic Requirements for Filing

To initiate the process, the petitioner must gather the following documentation:

PSA Marriage Certificate: The official record of the marriage.
PSA Birth Certificates: Of the spouses and any children born of the union.
Psychological Evaluation Report: Essential for Article 36 cases, conducted by a clinical psychologist or psychiatrist.
Affidavits of Witnesses: Statements from third parties who can attest to the breakdown of the marriage or the psychological state of the parties.
Proof of Residency: To establish the jurisdiction of the Regional Trial Court (RTC).
Inventory of Assets: A list of communal or conjugal properties and debts.

IV. The Legal Procedure

The process is rigorous and can take anywhere from two to five years, depending on the court's docket and the complexity of the case.

Step 1: Preparation and Filing

The petitioner, through counsel, files a verified Petition for Annulment/Nullity in the Regional Trial Court of the province or city where either the petitioner or the respondent has been residing for at least six months.

Step 2: Summons and Answer

The court issues a summons to the respondent. The respondent has 15 days (or 30 days if served by publication) to file an "Answer." If no answer is filed, the court cannot simply grant the petition by default; it must order the Public Prosecutor to investigate.

Step 3: Investigation by the Public Prosecutor

The Prosecutor (State Solicitor) conducts an investigation to determine if there is collusion between the parties (i.e., if they are working together to "fabricate" the annulment). If collusion is found, the case is dismissed.

Step 4: Pre-Trial Conference

The court sets a mandatory pre-trial. Here, the court considers the simplification of issues, the possibility of a stipulation of facts, and issues regarding child custody and support.

Step 5: The Trial

The petitioner presents evidence and witnesses (including the psychologist). The respondent may also present their own evidence. The Public Prosecutor remains present to ensure that evidence is not suppressed or fabricated.

Step 6: The Decision

The judge issues a Decision. If granted, the court will issue a Decree of Annulment/Nullity.

Step 7: Registration and Annotation

Once the decision is final and executory, it must be registered with the Local Civil Registrar where the marriage was recorded and the Philippine Statistics Authority (PSA). The marriage certificate will then carry an annotation stating the marriage is void or annulled.

V. Important Considerations

Cost: Legal fees, psychological evaluations, and filing fees can be substantial. Total costs often range from PHP 250,000 to over PHP 600,000.
Status of Children: Children born of voidable marriages or marriages declared void under Article 36 are considered legitimate.
Property Relations: The court will also rule on the liquidation, partition, and distribution of the properties owned by the spouses.