Legal separation (sometimes judicial separation, separate maintenance, divorce a mensa et thoro, or divorce from bed-and-board) is a legal process by which a married couple may formalize a marital separation while remaining legally married. A legal separation is granted in the form of a court order. In cases where children are involved, a court order of legal separation often makes child custody arrangements, specifying sole custody or shared parenting, as well as child support. Some couples obtain a legal separation as an alternative to a divorce, based on moral or religious objections to divorce.

Legal separation does not automatically lead to divorce. The couple might reconcile, in which case they do not have to do anything in order to continue their marriage.

Legal separation is a separation that is sanctioned by a court order, meaning that the spouses may legally live apart, but they are still legally married. The legitimacy of any future child born to the couple remains intact, and the spouses may not legally remarry. This type of separation allows the couple to live apart without concerns about being taken to court for "desertion". (In some jurisdictions, provable "desertion" is legal grounds for a divorce.)

There are several reasons why a couple might seek a legal separation. In some legal jurisdictions, including certain countries, it can be difficult to get a full and final divorce, but if the spouses are already legally separated for an extended period of time (for example, three years), the court may decide to grant a full and final divorce. When the requirements of burden of proof for a divorce are difficult to meet, in most jurisdictions, a legal separation ruling assures the couple a slot in the court's schedule whenever they file for a full divorce, by showing that they were both serious about their separation.

Sometimes, a legal separation is used when one partner is claimed to be emotionally, verbally, or physically abusive, keeping the marriage in existence while the two spouses are physically separated. This physical separation may give the two of them a chance to work out the problems in their relationship while residing in legally sanctioned separate dwellings. Spouses may also request a legal separation to protect themselves from accusations of desertion or abandonment—such as in cases where one must depart from the other for an extended period of time.

In Canada, "separation" is when a couple decides to live apart as a consequence of their relationship breaking down. This differs from the specific legal status of legal or judicial separation in some other jurisdictions, which requires filing with the courts. A mensa et thoro separation does not exist in most provinces, but the term "legal separation" is commonly used for a contract created between two spouses at the time of their separation, more properly referred to as a separation agreement, a legally binding written contract voluntarily signed by two spouses (either married or common law) who have separated.

However, the province of Saskatchewan does allow a legal separation under provincial law, which is distinct from a divorce under federal law. A legal separation in Saskatchewan can be granted by the Court of King's Bench.

In Ontario, a separation agreement is unenforceable unless it is made in writing, signed by the parties and witnessed. This written agreement usually resolves all issues arising from the separation, including custody and access, child support, spousal support and the division of property, except only a court can grant a divorce itself.