Today’s RF and Microwave engineers are confronted with IC and RF Board level design requirements that must be met in small footprint and highly dense packages. Proximity and coupling effects alter the performance and cause design failures. Predicting these coupling effects on your design prior to tape-out and fabrication is crucial. EM partitioning and EM/Circuit Co-simulation and Co-tuning with circuitsimulated components allow to bring back your output results into specification compliance earlier in the design flow to help achieve first pass success. This paper will describe the EM/Circuit Co-simulation and Co-tuning process and provide an example to illustrate how the process is performed.