In this thesis, means of personal right reinforcement of contractual obligation with an emphasis on the Croatian legal system will be studied. The legal characteristics of the bail institute and the institute of contractual penalty that increase the certainty of fulfillment of the debtor's obligation and reinforce the creditors situation will be elaborated. Suretyship (bail) provides increased certainty to the creditor that his claim will be settled because of the fact that, beside the debtor, another person (guarantor or surety) commits to fulfill the debtors commitment in the case that the debtor does not fulfill it on his own. Contractual penalty is a negative property consequence provided by contract and is directed towards the debtor in the case the debtor does not fulfill his obligation, fulfills it overdue or disorderly. The main feature of personal right reinforcements is their accessoriness, which means that they share the same faith of the primary obligation. Part of the thesis refers to the means of personal right reinforcement of contractual obligation in Roman law – bail, intercessio and stipulatio poenae. Furthermore, relevant court practices related to the suretyship and contractual penalty are being reviewed.