Long life signifies the well-being or higher living standard of a country. In modern era, life expectancy at birth has been considered as a key factor for the working age population and economic contribution in a country. The present study attempts to investigate the key determinates of life expectancy at birth among high, middle and low income countries. The empirical analysis is based on a panel of 50 countries over the period of 1990-2014. This impact has been examined for both aggregated and disaggregated level of samples by using dynamic Panel Autoregressive Distributive Lags Model (ARDL). The long run results obtained for the aggregated samples suggested that there existed negative relationship among life expectancy and Co2 emissions, population growth and urban population growth while positive relationship among life expectancy with other independent variables. The findings for the High Income Countries shows that in the long run there existed negative and significant relationship among life expectancy and Co2 emission, while other variables had positively and significantly related with life expectancy, on short run only health expenditure had shown divergence to their original path. In case of Middle Income Countries, in long run there exists negative relationship among life expectancy, disasters, and urban population growth, while other variables had shown positive effect on life expectancy. In short run only population growth shows that there exists a significant convergence. In case of Low Income Countries, the results suggested that there exists negative relationship in life expectancy with Co2 emission, disasters, and urban population growth. In contrast, there exist positive relationship among other variables with life expectancy. While coming to short run adjustment coefficients, no variable has shown the convergence to their mean paths in case of any shock. Supervisor:- Dr. Shujaat Farooq