This chapter provides an understanding of the fundamental principles and circuit modeling of WPT technology. WPT can be classified into near-field techniques utilizing electromagnetic induction and far-field techniques using electromagnetic radiation. Most current wireless charging technologies are based on inductive coupling. This chapter elaborates on the magnetic flux phenomenon in 2-coil inductive links and defines key parameters such as the coupling coefficient (k) and mutual inductance (M). It also covers the equivalent circuit model and efficient design considerations for 2-coil inductive links to optimize PTE and power delivered to load (PDL). Specifically, it emphasizes that the choice between series and parallel configurations for the Rx LC-tank depends on the Rx’s qulity (Q)-factor and the required voltage-current characteristics at the load. Furthermore, multi-coil systems like 3-coil and 4-coil inductive links are introduced, explaining how they can enhance WPT system efficiency and flexibility through improved impedance transformation and higher Q-factors, even under weak coupling conditions. Subsequently, the chapter analyzes the basic principles, design considerations, and common types of DC-AC converters (power amplifiers) essential for generating high-frequency AC current in the Tx coil in WPT systems. Finally, it discusses the role of AC-DC converters (rectifiers) in converting AC signals from the Rx LC-tank into DC power for the load, along with their various configurations.