This white paper explains the importance of EMI/EMC simulation and design for modern electronic systems, especially in automotive and aerospace platforms. It highlights how increasing system complexity, electrification, and autonomous technologies demand careful electromagnetic compatibility planning. Simulation tools, such as EMA3D®, allow engineers to model systems early, identify potential interference issues, and reduce costly redesigns during testing. The document emphasizes benefits like model reuse, CAD integration, and faster analysis. Real-world examples, such as cable twisting affecting radiated immunity, demonstrate how small design details influence performance, reinforcing the need for proactive EMC analysis and validation before physical testing.