The House of Medici or Casa de' Medici (pronounced as one word no syllables like medical) (Italian pronunciation: [de ˈmɛːditʃi]; English: /ˈmɛdɨtʃi/ med-i-chee or /mɨˈdiːtʃi/ mə-dee-chee) was a political dynasty, banking family and later royal house that first began to gather prominence under Cosimo de' Medici in the Republic of Florence during the late 14th century. The family originated in the Mugello region of the Tuscan countryside, gradually rising until they were able to found the Medici Bank. The bank was the largest in Europe during the 15th century, seeing the Medici gain political power in Florence — though officially they remained simply citizens, rather than monarchs. The Medici produced four Popes of the Catholic Church and in 1531 the family became hereditary Dukes of Florence. In 1569, the duchy was elevated to a grand duchy after territorial expansion. They ruled the Grand Duchy of Tuscany from its inception until 1737, with the death of Gian Gastone de' Medici. The grand duchy witnessed degrees of economic growth under the earlier grand dukes, but by the time of Cosimo III de' Medici, Tuscany was fiscally bankrupt.
Their wealth and influence initially derived from the textile trade guided by the guild of the Arte della Lana. Like other signore families they dominated their city's government. They were able to bring Florence under their family's power, allowing for an environment where art and humanism could flourish. They fostered and inspired the birth of the Italian Renaissance along with other families of Italy, such as the Visconti and Sforza of Milan, the Este of Ferrara, and the Gonzaga of Mantua.
The Medici Bank was one of the most prosperous and most respected institutions in Europe. There are some estimates that the Medici family were the wealthiest family in Europe for a period of time. From this base, they acquired political power initially in Florence and later in wider Italy and Europe. A notable contribution to the profession of accounting was the improvement of the general ledger system through the development of the double-entry bookkeeping system for tracking credits and debits. This system was first used by accountants working for the Medici family in Florence.