The growing inequality in the global economy across the planet is reaching unprecedented levels. This book seeks to develop frameworks for the assessment of excessive inequality and its impact on social-economic progress and sustainable development. It begins by summarizing the theoretical approaches of economic inequality, its specificity, and questioning what economic inequality really is and how it progresses. Next, the book explores issues of methodology for addressing the growing excessive economic inequality. It then applies these concepts to examine inequality across a range of the European Union (EU) countries. A variety of factors are considered, such as the impact of economic inequality on socio-economic progress, when normal inequality turns into excessive inequality, and its impact on economic growth, quality of life, and the environmental sustainability across different groups.