Ignazio Busca (August 31, 1731 in Milan – August 12, 1803 in Rome) was an Italian cardinal and Secretary of State of the Holy See. He was the last son of Lodovico Busca, marquess of Lomagna and Bianca Arconati Visconti. he took a degree in utroque iure in 1759 at the Università La Sapienza of Rome. Relator of the Sacred Consulta and referendary of the tribunal of the Apostolic Signature, he was ordained priest on August 20, 1775. Elected titular archbishop of Emesa, he was consecrated on September 17, 1775 in Frascati, by Henry Benedict Stuart. He was apostolic nuncio in Flanders and apostolic vicar for Netherlands from 1776 to 1785 and later was governor of Rome from 1785 until 1789. Created cardinal in the consistory of March 30, 1789, he received the Galero and the title of Santa Maria