Thesis: This thesis consists of four chapters on income distribution. All chapters are interrelated, and cohesively they serve the sole purpose of discussing the concept of income composition inequality. This concept is thoroughly explored from a conceptual, mathematical, as well as political economy perspective. Chapter 1 introduces this dissertation and its main findings. Chapter 2 presents the concept of income composition inequality, together with a summary statistics for its technical assessment. Chapter 3 analyzes the determinants of income inequality variation in light of the novel inequality dimension previously introduced. Chapter 4 studies the evolution of income composition inequality in Italy between 1989 and 2016. Chapter 5 proposes a method to jointly analyze the distributions of capital and labor and of saving and consumption across the population. This method hinges on the concept of income composition inequality. Finally, Chapter 6 concludes this dissertation and lays the ground for future research on the matter.