This book provides a general framework for the use of theoretical contributions in empirical works, addressing the question of what is the effect of a price change on household well-being. This simple question is one of the most relevant and controversial questions in microeconomic theory and one of the main sources of errors in empirical economics. In particular, this book aims to 1) Review the essential microeconomics literature since the first seminal papers by Hicks in the 1930s; 2) Organize and simplify this literature in a way that can be easily used by analysts with different backgrounds providing algebraic, geometric and computational illustrations; 3) identify and