Annulment of marriage can occur when the marriage is voidable or is invalid.
Unlike with divorce, once an annulment takes place the marriage is generally treated as if it had never happened.  Annulment can only occur under very strict guidelines, and is rarely possible.
In order to prove a marriage in California is able to be annulled (invalid after the court order) or voided (never valid), one of the following grounds for Nullity must be proven beyond a reasonable doubt (a difficult standard proof):

  1. Incestuous Marriage
  2. Physical Incapacity and concealment of inability to enter into marital relations
  3. Bigamous Marriage
  4. Petitioner was under the Age of 18  at time of marriage and lacked the legal capacity to marry (unless they obtain parental consent);
  5. Fraud
  6. Unsound Mind
  7. Forced Consent

Nullity of Marriage and Annulment,  rarely if ever happens because the grounds are difficult to prove and/or the time and cost to process is much greater than dissolution of marriage (more commonly referred to as a divorce).