This paper presents the topic Nullity of legal transactions. Along with voidable legal transactions, they represent a form of invalid legal transactions. The main feature of null legal transactions is that they do not produce the legal effects that they would if they were valid. Moreover, it is taken as if they were not even concluded. After defining the concept of nullity, the paper analyzed the causes that lead to nullity; impossibility, inadmissibility, indeterminacy and indeterminacy of the act, business incapacity, invalidity and inconsistency of declaration of will, inadmissibility of motive and lack of necessary form. Furthermore, the concepts of partial invalidity, convalidation and conversion of null legal transactions are discussed. Also, the paper provides an insight into the consequences of nullity. Namely, even though they are null, legal transactions still produce unintended legal effects, which we call the consequences of nullity. These consequences are the restoration to original condition (restitutio in integrum) and liability for damage. The purpose of the restoration to original condition is to establish the state that existed before the performance of the act by the creditor, and therefore each of the contractual parties is obliged to return to the other party everything that it received on the basis of the contract in question. On the other hand, in order for the claim for damages to be realized, it is necessary to cumulatively fulfill the following assumptions: the guilt of one party for entering into a void contract, the existence of a causal connection (cause) between the concluded contract and the damage, and the conscientiousness of the injured party. At the end of the paper, it was explained who are the persons authorized to assert nullity and was pointed out that nullity can be asserted indefinitely.