How do you design circuits for electromagnetic compatibility (EMC)?

EMC design considers both emissions and susceptibility. Techniques include: proper grounding (star, single-point, or ground planes), decoupling capacitors at IC power pins, controlled impedance traces, shielding enclosures with proper seam and aperture treatment, filtering at I/O ports, rise-time control (slower edges reduce high-frequency content), and differential signaling. PCB layout minimizes loop areas for magnetic coupling. Pre-compliance testing guides design iterations before expensive formal testing.