Just living apart, or having a written agreement to live apart, or getting a court order approving living apart. If you or your marriage partner decides to go your separate way, you don't need an agreement or a court order to make your separation legal. Just the fact that one of you moves out makes it a separation under the law. One year from the date of separation you will be able to get a divorce based on that separation. In most cases, one party must be a resident.
Some states have no statutory provision at all.
In other countries, one party must be a legal resident for at least six months. For a timetable of US residency requirements, go here . For criteria to file in the Netherlands, click here . For other areas in the US and Canada, visit Divorce Source . In most localities, each side must seek separate representation.