The emergence of double entry bookkeeping marked the shift in bookkeeping from a mechanical task to a skilled craft, and represented the beginnings of the accounting profession. This study seeks to identify what caused this significant change in bookkeeping practice. I do so by adopting a new accounting history perspective to investigate the circumstances surrounding the emergence of double entry in early 13th century Italy. Contrary to previous findings, this paper concludes that the most likely form of enterprise where bookkeeping of this form emerged is a bank, most likely in Florence. Accountability of the local bankers in Florence to the Bankers Guild provided a unique external impetus to generate a new form of bookkeeping. This new bookkeeping format provided a clear and unambiguous picture of the accounts of all debtors and creditors, along with the means to check that the entries between them were complete and accurate.