There are many different kinds of contracts that can be used in Dom/sub (D/s) relationships.  Basically they are put in place by both the Dominant and the submissive and individualised to suit their needs and desires, and to define the limits of the relationship.  A 'BDSM' contract is not a legal document and will not stand up in a court of law so due care should be taken when agreeing and consenting to have one in place.   This is a binding agreement between two consenting adults, based on the limits of both the Dominant and the submissive.

A contract can be put in place for a set period of time and can be negotiated at set times and changed by mutual agreement.  The limits of a contract can vary and can extend into different areas of BDSM and service, and can be added to at times as improvement of service is learned.   Common clauses in a contract are: health, safety, sexuality, openess, dependants, discipline, limits, and finance.   All of these are common practice but are usually individual to specific tastes and limits.

Contracts are almost always in place between Master/Mistress and slave, and often used for Dominant and submissives. 

Here are 2 examples of lifestyle contracts :

 Dominant and submissive Master/Mistress and slave