This paper presents a conceptual framework of auditing firms, previous research on auditing firms, and empirical results about the question whether the Big Four firms are dominant in the banking sector of the European Union. Analysing the data of the 3,056 banks registered in the EU, this study shows which the audit companies dominate in the financial markets, and that the presence of other audit firms is higher than the presence of the Big Four firms. The results show that there are countries in which the audit firm is in cooperation with other audit firm in audit engagement. This paper presents a clear picture of competitors in the audit market, as well as their role in auditing of the banks financial statements.