In the post-war period the banking system in Poland underwent two important system transitions: after 1946 and after 1989. The third transformation began after May 1, 2004, but it did not have a systemic character. The Polish banking sector started to operate on the Single European Market. The first part of the paper is devoted to the problems of the banks' transformations after 1989 with a special focus on the quantitative development of banks in 1989-2008, and on subsequent privatisation and consolidation processes. The former intensified in 1989-1999, and the latter in 1999-2002. The consolidation process was very noticeable in the sector of cooperative banks after 1994. The second part of the paper includes an economic and financial analysis of the banks. A lot of attention was paid to the liquidity of the banking sector. It was assessed as good, which was confirmed by a short-term rating of Moody's and by the Financial Stability Report 2009, published by the National Bank of Poland in June 2009. The comparison of the net profit of the banking sector in 1997-2008 shows its dependence on the economic situation and policy. The number of banks with capital adequacy ratio well above the minimum required by the banking supervision is rising. The financial power ratings are not favorable for the domestic banks. The third part of the paper focuses on the development directions of the Polish banking sector. It may be concluded on the basis of the analysis that privatisation and consolidation processes will be continued. They will concentrate on the capital of foreign banks already operating in Poland. As compared with individual foreign banks, the potential of the Polish banking sector is week. The fourth part of the paper focuses on the presentation Polish banking sector in the context of European Union banking sector. The paper finishes with conclusions. Generally, Polish banks have to implement a strategy to enable them to compete on the Single European Market, i.e. to look for new revenue sources, to reduce costs and improve their loan portfolios. The comparison of selected aspects of the Polish banking sector in the most developed EU Member States shows that the differences are still too large. Therefore, it seems correct to claim that the Polish banking system is undergoing another transition. It is adjustment to the Single European Market.