It used to be very common for parties to Separate before filing for Divorce because the separation served as grounds for divorce after the parties lived separate and apart for a period of one year. Today, New York State is a No Fault Divorce state and Separation has become less common. There are two ways to get legally separated in New York State, by executing a formal Separation Agreement, or by suing for a Judgment of Separation.
The Separation Agreement is a detailed written agreement that should be prepared by an Attorney. The agreement says that the parties will live separate and apart according to the agreement with respect to Child Support, Maintenance Custody, Visitation, and the Division of Marital Property. The Separation Agreement is signed and is filed with the County Clerk. After one year passes, the separation agreement may serve as grounds to convert the separation into a divorce.
Another form of separation in New York is through a Judgment of Separation granted by the Supreme Court. This is basicly the same as a contested divorce, but you are only separated at the end of the process. This judgment is based on having grounds for separation (see DRL §200). One year after the entry of the Judgment of Separation, either spouse may sue for a divorce, based upon conversion grounds.