The present paper shows the results of an empirical study to prove that income inequality has increased over the past decades. To conduct the study, an income inequality dataset containing 133 countries over the 1990-2014 period was created. The results indicate that globally, income inequality (population-weighted Gini coefficients), on average, increased from 38.6 to 41.8 during that period. They further show the existence of variations in the level of income inequality across regions and groups of countries. The reduction in income inequality, among others, remains one of the key challenges associated with the 2030 Agenda for Sustainable Development. Therefore, in this paper, various transmission mechanisms and drivers of the increasing level of income inequality are identified and possible forward-looking development policies to reduce income inequality are given.