Sukuk (Arabic: صكوك, romanized: ṣukūk; plural of Arabic: صك, romanized: ṣakk, lit. 'legal instrument, deed, cheque') is the Arabic name for financial certificates, also commonly referred to as "sharia compliant" bonds. Sukuk are defined by the AAOIFI (Accounting and Auditing Organization for Islamic Financial Institutions) as "securities of equal denomination representing individual ownership interests in a portfolio of eligible existing or future assets." The Fiqh academy of the OIC legitimized the use of sukuk in February 1988.

Sukuk were developed as an alternative to conventional bonds, which are not considered permissible by many Muslims as they pay interest (prohibited or discouraged as Riba, or usury), and also may finance businesses involved in activities not permitted under sharia (gambling, alcohol, pork, etc.). Sukuk securities are structured to comply with sharia by paying profit, not interest—generally by involving a tangible asset in the investment. For example, sukuk securities may have partial ownership of a property built by the investment company (and held in a Special Purpose Vehicle), so that sukuk holders can collect the property's profit as rent (which is allowed under Islamic law). Because they represent ownership of real assets and (at least in theory) do not guarantee repayment of initial investment, sukuk resemble equity instruments, but like a bond (and unlike equity) regular payments cease upon their expiration. However, most sukuk are "asset-based" rather than "asset-backed"—their assets are not truly owned by their Special Purpose Vehicle, and their holders have recourse to the originator if there is a shortfall in payments.

Different types of sukuk are based on different types of Islamic contract (murabaha, ijarah, istisna, musharaka, istithmar, etc.) depending on the project the sukuk is financing.

According to the State of the Global Islamic Economy Report 2016/17, of the $2.004 trillion of assets being managed in a sharia compliant manner in 2014, $342 billion were sukuk, being made up of 2,354 sukuk issues.

The Arabic term ṣakk was borrowed from Classical Persian چک (čak, “legal document, document, contract, deed of sale, bill”).

In the classical period of Islam, sakk (sukuk) meant any document representing a contract or conveyance of rights, obligations or monies done in conformity with Shariah.^{[citation needed]} The term was used to refer to financial obligations originating from trade and other commercial activities in the Islamic pre-modern period.

According to Camille Paldi, the first sukuk transaction took place in Damascus in its Great Mosque in the 7th century AD. Muslim traders are known to have used the cheque or ṣakk system since the time of Harun al-Rashid (9th century) of the Abbasid Caliphate.

The modern Western word "cheque" appears to have been derived from "sakk" (singular of sukuk), which during the Middle Ages referred to a written agreement "to pay for goods when they were delivered" and was used to "avoid money having to be transported across dangerous terrain".