In this chapter, we explore the energy-participation ratio (EPR) method, a pivotal technique for quantizing and analyzing superconducting circuits. The EPR method enables us to systematically quantify how energy is distributed across different components and vibrational modes in a physical system, such as superconducting qubits, resonators, or coupled systems. While the method has roots in the study of mechanical and vibrational systems, its application to electromagnetic structures—like resonators, cavities, and Josephson circuits—has been transformative. By identifying and quantifying the contribution of each mode to the total energy, the EPR method serves as a critical tool for understanding system dynamics, optimizing circuit designs, and enabling accurate quantization. This chapter demonstrates how the EPR method is applied to superconducting circuits, both conceptually and practically, with an emphasis on its implementation in Qiskit Metal, a comprehensive framework for modeling and simulating superconducting qubits.