In this chapter, we will discuss a comprehensive modeling approach to analyze multiport resonant converter operations and the process to synthesize the optimal control variables to track best efficiency metrics at wide loading and voltage gain conditions. For example, in two-port resonant converters like LLC, CLL, and CLLC consisting of full-bridge architectures, there are four control degrees of freedom that include phase shift angle, two full-bridge voltage duty ratios, and switching frequency, while for three-port resonant converter the number of control variables increases to six. So, fundamentally it is crucial to understand the power flow and voltage gain formulation as a function of the control variables, and then to establish the power loss modeling and soft-switching constraints that determine the voltage regulation and efficiency performance of the converter. This chapter specifically addresses the modeling and optimization of two-port CLLC and three-port C3L3 converters, with principles that are broadly applicable to other resonant converter types.