The thesis at hand deals with nullity and avoidance of legal transactions. The analysis starts in the Roman Law. Though, an actual science of legal invalidity was unforeign at that time. Nevertheless Romans had indeed accomplished certain casuistic provisions relating to that matter. At the beginning, civil nullity was the dominant picture but, supported by praetorian development of law, avoidance became increasingly more distinct. In the subsequent centuries there had not been any considerable developments in the analysis of invalidity. Natural law, with its theory of legal transactions, and the codifications at that time accomplished a new momentum to the invalidity. This paper lists the facts of nullity and avoidance found in the early codifications, like the Codex Maximilianeus or the Prussian Civil Code, right up to the Austrian General Civil Code. Following this, the doctrines of Savigny, Puchta, Windscheid and Dernburg, that had an important impact on the origin of the German Civil Code, managed a decisive breakthrough in the examined matter. Finally the current Austrian theory of invalidity is dealt with, which core assertions still correspond to those made from the historical legislator of 1811.