This research aims to study the relationship between economic performance, economic reforms, corruption, ethnic diversity and business environment. In chapter two, meta-analysis and meta-regression analysis methods are applied to study the relationship between economic growth and corruption. This shows that despite severe publication bias, there seems to be a genuine negative effect of corruption on growth. This impact is systematically affected by whether the authors are academics and whether the study controls for endogeneity and heterogeneity. As for mechanisms, the findings show that corruption significantly undermines the positive influence of institutions and trade openness on economic growth. Chapter three investigates the effect of dynamic ethnic diversity as endogenous variable on economic growth in the transition context. For this purpose, a unique data set is constructed based mostly on primary data (national censuses). Once diversity is instrumented; it shows a significant negative impact on economic growth which is robust to different specifications, polarization measures, econometric estimators, as well as to the use of an index of ethnic-religious-linguistic fractionalization. Chapter four provides evidence of the role of economic reforms on economic performance in developing countries measured by economic growth and industrial growth. This research focuses on, and constructs individual indicators for the following reforms: external stability, macroeconomic stability, financial development, trade liberalization and institutional quality. The main finding is that economic reforms strongly support growth in the long-run. They mostly have mixed effects in the short-run. Moreover, institutions are imperative to boost economic performance over the long run. Finally, chapter five demonstrates the relationship between firm performance and business environment, ownership, competition and exports in Syrian industrial private sector. Performance is measured in level and growth variables. The main findings show that firm performance is positively boosted by finance and technology and hindered by poor investment climate, in particular, corruption. However, competition and foreign ownership seem to not have first-order effects.