Formerly, a letter sent by one party to a civil action, in which a remedy other than debt or damages is claimed, to another offering to compromise the action on terms specified in the letter. The first such letter was sent in the case Calderbank v Calderbank  Fam 93 (CA). Calderbank offers are now (since the introduction of the Civil Procedure Rules in 1999) generally known as Part 36 offers. However, the term remains in use in family proceedings. Calderbank letters may be referred to only when the question of costs rises.