This dissertation examines the role of Cardinal Giovanni Battista de Luca in the reform of nepotism in the seventeenth-century Catholic Church. Popes gave very large amounts of money to their relatives and the burden of nepotism on the Catholic Church was very onerous. The Catholic Church was crippled by nepotism and unable to carry out its traditional functions. Although Cardinal de Luca and Pope Innocent XI worked tirelessly to end nepotism, they were thwarted in their attempts by apprehension among the Cardinals concerning conciliarism and concerning the use of reform measures from the Council of Trent; by Gallicanism and the attempts of the French King to exercise power over the French Church; and by the entrenchment of nepotism and its long acceptance within the Church. Cardinal de Luca and Innocent XI were not able to push through reforms during their lifetimes but Pope Innocent XII was able to complete this reform and pass a reform Bull. This dissertation has two complementary themes. First, a confluence of circumstances allowed for the unfettered growth of nepotism in the seventeenth-century Church to the point of threatening the well-being of the Catholic Church. Reform was not undertaken until the threat to Church finances was severe. Secondly, two upstanding and honest reformers arose in the Catholic Church to correct the problem, de Luca and Innocent XI. The achievements of Cardinal de Luca, also an important reformer of the Canon Law, are almost unknown to an English-speaking audience.