This Thesis shall elaborate in detail on defects in consent, placing a specific emphasis on error and fraud. The first part shall explain defects in consent, how they influence a legal transaction, what prerequisites must be met and what the consequences are of concluding legal transactions in which defects in consent are present. Furthermore, special attention shall be paid to error being one of the defects in consent, what types of errors exist and what the consequences are of concluding legal transactions in which defects in consent are present. Following this, fraud occurring between contracting parties shall be explained in greater detail. The fraudulent behaviour of a third party not being a party to such contracts shall also be examined. This shall then be followed by an analysis of the notion of voidance resulting from concluding such contracts in which error and fraud are present. The concept of convalidation shall also be explained, in addition to the consequences of voidance: compensation of damages and a reinstatement to the prior state of affairs. The final part of this Thesis shall list several examples of case law from the Republic of Croatia which show how litigations occurred as a result of error or fraud and were resolved in case law.