This entry provides an analysis of the kafalah (guarantee) in Islamic law, a secondary security agreement rooted in mutual aid (hasbiyyah) that enhances financial stability. The distinction between property guarantees (al-kafāla bi’l-māl)—covering debts or goods—and personal sureties (al-kafāla bi’l-nafs) is paramount. Historically, the guarantee was considered a gratuitous act of social charity (tabarruʿ). However, it has evolved into a modern form within the context of institutional finance. While classical doctrine proscribed the levying of fees, contemporary participatory banking legitimizes the imposition of commissions as “service fees.” This transition from individual assistance to a guarantee system exemplifies Islamic finance’s dynamic adaptation to global trade requirements.