Guarantee and suretyship are similar concepts but have key distinctions. A guarantee is collateral and the guarantor is primarily liable, while suretyship is an original undertaking and the surety is secondarily liable. The guarantor promises to pay if the principal debtor defaults, while the surety undertakes to pay the debt if the principal does not pay. The guarantor insures the solvency of the debtor, whereas the surety insures the debt itself.