This thesis investigates several aspects concerning the financial stability of Islamic and conventional banks. This is important because the strong growth of Islamic banking, notwithstanding their marked uniqueness in operational and financing behaviour, combined with fierce global competition with the prevailing conventional bank system, raises concerns among regulators and practitioners about the long-run sustainability of Islamic banking. First, the thesis compares the level of financial stability in Islamic and conventional banks using three different methods of credit risk measurement. Second, it compares the effect of competition on stability across Islamic and conventional banks. Finally, it investigates whether efficiency significantly modulates the linkage between competition and stability in both Islamic and conventional banks. In the first research question, the thesis considers the levels of credit risk in Islamic and conventional banks, for which existing literature finds no conclusive result. One problem with existing studies is the use of accounting information alone to assess credit risk and this could be especially misleading with Islamic banking. Using a market-based credit risk measure, namely, Merton’s distance-to-default (DD) model, we evaluate the credit risk of 156 conventional and 37 Islamic banks across 13 countries between 2000 and 2012. We also calculate the accounting information-based Z-score and nonperforming loan (NPL) ratio for the purpose of comparison. The results show that Islamic banks have significantly lower credit risk than conventional banks as based on DD. In contrast, and as expected, Islamic banks display much higher credit risk using the Z-score and NPL ratio. These findings suggest that the measure chosen plays a significant role in assessing the actual credit risk of Islamic banks.