A legal separation does not end a marriage or domestic partnership. You can't marry or enter into a partnership with someone else if you are legally separated (and not divorced). A legal separation is for couples that do not want to get divorced but want to live apart and decide on money, property, and parenting issues. Couples sometimes prefer separation for religious reasons.
If you file for a legal separation, you may later be able to file an amended petition to ask the court for a divorce.
In a legal separation case, you can ask the judge for orders like child support, spousal support, partner support, custody and visitation, domestic violence restraining orders, or any other orders you can get with a divorce case.
An annulment (or "nullity of marriage" or "nullity of domestic partnership") is when a court says your marriage or domestic partnership is NOT legally valid. A marriage or domestic partnership that is incestuous or bigamous is never valid. Other marriages and partnerships can be declared "void" because of force, fraud, or physical or mental incapacity; one of the spouses or partners was too young to legally marry or enter into a domestic partnership; or one of the spouses or partners was already married or in a registered domestic partnership.
Annulments are very rare. If you ask to have your marriage or domestic partnership annulled, you will have to go to hearing with a judge.
What about the children?
If you have children in common with the other party, you must ask the court to establish the parentage of that person. Check with a lawyer about how to do this.
What about domestic partnerships?
In California, starting on January 1, 2005, domestic partners must also file for dissolution, legal separation, or annulment to end their relationship.