Textbook in PDF format This book introduces the theory behind the incoherent scattering of electromagnetic waves (radar waves) by free electrons—a key technique for studying critical parameters of the Earth’s ionosphere. Starting with scattering by statistically independent electrons, including magnetized cases, the book progressively develops a comprehensive model. This framework is extended to include ‘dressed particles’, accounting for long-range Coulomb interactions between charged particles. A consistent approach to incorporating particle collisions is presented, with an example of charge exchange interactions for illustration. Appendices provide essential background material, ensuring the content is accessible to readers