Responding to a common concern, Lagges points out that children of an annulled marriage aren't considered illegitimate. Though a Decree of Nullity (as annulment is formally known) establishes that the marriage was never valid in the sacramental sense, their one-time civil marriage is sufficient for legitimacy, and annulment can't affect children's status retroactively.
Official Stance on Divorce: "The Church, after an examination of the situation by the competent ecclesiastical tribunal, can declare the nullity of a marriage, i.e., that the marriage never existed. In this case the contracting parties are free to marry." (From the Catechism of the Catholic Church)
True marriage is permanent, but we often fall short of our potential. Divorce itself is not a sin in Catholicism, but remarriage is not permitted without an annulment. Individuals who are divorced and remarried without annulment are not permitted to receive the Eucharist (Holy Communion). Annulment frees remarried individuals to participate in the sacraments and thus fully realize their relationship with God despite their previous failings.
When? After a civil divorce is granted. Often, participants wait until they are about to remarry before considering an annulment. Most pastors urge individuals to consider it as soon as they feel ready, rather than waiting.
Where? At home, in your pastor's office, and/or the offices of your diocese's marriage tribunal. In the rare instance that annulment is denied, you can appeal to a higher jurisdictional (city, provincial, state, or national) level. In some special cases, either party may have the right to petition the highest appeal court in Rome (the Roman Rota).
Who Participates? Annulment can be initiated by either spouse, but both may be asked to testify. The spouse's pastor will be the contact person, though the annulment itself is processed by a marriage tribunal at the archdiocese level. Individuals and couples can also seek the counsel of priests and laypeople who are expert in the annulment system.
Children don't usually participate or testify, but if they're old enough to understand the civil divorce and have some understanding of Catholic traditions, you can discuss what annulment means and how it affects your relationship with them (and theirs with the Church). Making time to sit down together with your pastor may help resolve any questions they may have and ensure that they don't develop bitter feelings about the confusing and painful process they see their parents going through.
There is no public ceremony to mark annulment. The initiating spouse, and sometimes both spouses, are generally informed of the progress of their application by their pastor, who can also provide assistance in filling out the required forms.
Annulments are granted on one of many "official" grounds. These focus on the ability of the spouses to agree to specific Catholic views on marriage. If, at the time of your marriage, you failed to fully understand the Catholic view of the permanency or exclusivity of marriage, you might have grounds for annulment. The same holds true if you married on some condition, for example, that you'd live in a specific city or have a certain number of children.
Annulment may be easier to obtain if you have friends or family members who knew you at the time, who can testify to your claim. Even if the "obvious" causes for the marriage ending didn't surface until later--like if one partner has had an affair--these can often be tied to earlier flaws that may not have been obvious at the time of marriage.
The first step towards annulment takes place at home, in privacy, filling out paperwork, which may vary from diocese to diocese. Just as in a civil court case, you're asked to provide information about the particulars of your marriage--but in this case, the tribunal is also looking for information about your courtship and the marriage breakdown as well. Then, there is usually an interview at the tribunal's offices, which can take up to several hours, depending on the details involved. The tribunal takes over from there, calling in your ex-spouse if available, along with two or three witnesses, and possibly consulting with professionals (psychologists or counselors), if they see fit.