A contract of suretyship is a type of personal enhancement of the contractual relationship. It is concluded by the creditor and the guarantor, whereby the guarantor undertakes to the creditor to fulfill the valid and due obligation of the principal debtor if they fail to do so. It is concluded in writing, and only a person with full legal capacity can assume the guarantee. There are two main characteristics of a guarantee agreement. Accessoriness means that the guarantee agreement is a secondary contract, and its legal fate depends on and follows the legal fate of the main contract between the creditor and the principal debtor. When the debtor's obligation ceases, so does the guarantor's obligation. Subsidiarity implies the creditor's authorization to turn to the guarantor for fulfillment only after unsuccessfully attempting to recover from the debtor, unless joint liability is agreed upon, in which case the guarantor is liabile same as debtor. Suretyship can be provided for any valid obligation, as well as for conditional and specific future obligations. It can also be provided for the obligation of the guarantor themselves (sub-suretyship). The fundamental rule is that the guarantor's obligation is equal to the obligation of the principal debtor. Unless otherwise agreed, the guarantor is liable for the entire amount of the obligation, for the expenses incurred by the creditor in debt collection from the debtor, agreed interest from the date of payment, and for any increase in the obligation due to the debtor's delay or fault. Finally, when the guarantor fulfills the creditor's claim, he will become the new creditor and the claim transfers to him, acquiring the right of recourse from the principal debtor, enabling him to demand reimbursement for everything paid on his behalf.