The complexity of current EMC problems and the necessity to solve them in an accurate, reliable and efficient way require various analysis techniques. Numerical simulations can be considered as one of the most powerful tools for performing EMC analysis. Computational electromagnetics is used within basic research for example at universities as well as during nearly all phases of a product or system development process occurring in industrial life. Especially here, several challenges result from the application of numerical simulations. The most important ones are described and discussed in this paper. An exemplary interference problem is presented demonstrating the relevance and impact of those challenges.