This thesis deals with null decisions of the general meeting of a joint-stock company and its effects on the company. Firstly, the meaning of a general meeting's decision is explained and types of faulty decisions are mentioned. It is stated that reasons for null decisions are determined by law as numerus clausus, meaning there can be no other reasons. Different reasons for null decisions are explained by chapters, such as faulty convocation of the general meeting, omissions concerning the record, violations concerning the content of decisions, violations of morality, nullity based on court's decisions, then there are reasons concerning the election of the supervisory board and determination of annual financial reports, and there's a special case of the management board not consulting with the workers' council before a decision. Furthermore, other matters addressed include the removal of effects of nullity despite reasons for nullity, effects of nullity and the lawsuit for determination of nullity. Finally, matters of procedure are discussed, such as jurisdiction, determination of the value of the subject of dispute, burden of proof, interim measures and cases of registering decisions in the court registry before the court's final decision. Certain court cases are used where it is necessary to clarify the rules concerning nullity.