I am delighted to introduce this Mini-Special Issue of the IEEE Transactions on Microwave Theory and Techniques (TMTT), which showcases selected papers from the International Conference on Numerical Electromagnetics, Multiphysics Modeling and Optimization (NEMO 2023). The NEMO 2023 took place on June 28–30, 2023 at the historic Fort Garry Hotel in the heart of Winnipeg, MB, Canada. NEMO is an annual international event founded in 2014 and has become a popular venue for exchanging novel ideas in computational and applied electromagnetics, multiphysics simulations, and optimization methods. Alternating between North America, Asia, and Europe, the conference brings together leading experts from academia and industry within the IEEE Microwave Theory and Techniques Society (IEEE MTT-S) and beyond. In particular, broad participation was achieved this year due to the availability of both online and in-person formats for attendance. The participants of the NEMO 2023 had the opportunity to attend the technical sessions and social events and to establish closer personal contacts. The NEMO 2023 was sponsored by the Price Faculty of Engineering, University of Manitoba, Winnipeg, MB, Canada, and industry partners Xpeedic, Ansys, CEMWorks, and Sonnet Software.