Maria Theresa of Austria was, with Frederick the Great, certainly one of the most important figures in European history. In this paper, I will essentially only discuss the very first period in which the Austrian imperial army was, in the proper sense, 'Theresian', i.e. from 1740 until the end of the 'Eight Years' War', i.e. 1748. A particularly tragic aspect of that period was that a woman, Maria Theresa, originally certainly unaccustomed to anything when it came to the business of warfare, was forced by extraordinary circumstances to treasure her father's inheritance on her own. As time went by, however, she became so attached to her army that, after her husband's death, when she handed over the military 'keys' to her son, she said: "This branch of state administration was the only one in which I was really interested." All other topics and the bibliography will be completed in the second volume.