This book focuses on the advantages and disadvantages of each of the commonly used quantitative proteomic methods in terms of accuracy, sensitivity, and reproducibility. It also concentrates on the effective applications of these methods that resulted in many discoveries of the role of the proteins expressed in living cells and biological fluids. The first part of the book focuses on the description of advantages and disadvantages of each of the commonly used quantitative proteomic methods in terms of accuracy, sensitivity, and, especially, reproducibility. The second part of the book focuses on providing concise descriptions of the effective applications of these methods to demonstrate how they have resulted in many important discoveries of the roles of the proteins expressed in living cells.