A contract (aqd) which is incidental or auxiliary to another contract (usually a principal contract). Accessory contracts are mainly used for assuring the performance of other contracts, either by the same parties or by third-parties.

Examples of accessory contracts include agency (wakalah/wikalah), suretyship (kafalah/kifalah), pledge (rahn), etc.

Accessory contracts are known in Arabic as al-uqud al-tabayyeah (العقود التبعية).