Annulment and nullity of marriage are two institutions that function in two separate and independent legal systems. Despite some similarities, they cannot be used interchangeably. The differences between the annulment and declaring nullityof marriage follow mainly from the fact that the canonical marriage between baptized persons is a sacrament, a lifelong and indissoluble bond. For this reason, once validly contracted, it cannot be annulled or dissolved by divorce, but only bythe death of a spouse or a dispensation from an unconsummated marriage and the privilege of faith. In the case when marriage is contracted, despite the existence of impediments to marriage, the ecclesiastical tribunal, after completing the relevant proceedings, declares its nullity whereby this judgment is of a declarative nature. In the case of annulment of marriage, the legislator provided for some restriction as to the persons authorized to file a claim, and it also listed the situations in which, even though marriage was contracted in breach of law, its annulment is not possible. Therefore, convalidation by force of law is permissible. Such validation and such restrictions have not been provided by the ecclesiastical legislator, although the convalidation of marriage is possible as long as the matrimonial consent continues and some additional conditions have been satisfied. The judgment regarding the annulment of marriage is constitutive, although the effects of annulment have retroactive effects, whereby the legislator stated that for certain relationships, the rules of divorce shall be applicable. Both in the state and canonical orders, there are three groups of reasons that are the basis for annulment and declaration of nullity of marriage. These are impediments to marriage, defects to the declarations of intention of the spousesand defects to the mandate to contract marriage. The individual reasons have been briefly discussed to present the differences in their understanding under canon law and state law.