This chapter explores the fundamental phenomena of reflection and refraction of electromagnetic waves at interfaces between different media. It begins by deriving the continuity equations for the normal components of the electric displacement ( \(\textbf{D}\) ) and magnetic field ( \(\textbf{B}\) ), and the tangential components of the electric field ( \(\textbf{E}\) ) and magnetic excitation ( \(\textbf{H}\) ), directly from Maxwell’s equations. These continuity conditions are crucial for understanding how fields behave at boundaries. The core of the chapter lies in the derivation of the laws of reflection and refraction (Snell–Descartes law) as a direct consequence of these continuity conditions. It demonstrates that the frequency of the wave remains unchanged upon reflection and refraction, and that the incident, reflected, and transmitted wave vectors lie in the same plane. The special case of total internal reflection is discussed, highlighting its importance in applications like optical fibers. The chapter then introduces Fresnel’s reflection and transmission coefficients, which quantify the amplitudes of reflected and transmitted electric fields for both s-polarized (perpendicular) and p-polarized (parallel) incident waves. It shows how these coefficients depend on the angles of incidence and the refractive indices of the media. The concept of Brewster’s angle is presented, where p-polarized light experiences no reflection, leading to the phenomenon of polarization by reflection. Furthermore, the chapter defines reflectance and transmittance as the fractions of incident energy flux that are reflected and transmitted, respectively, and establishes their relationship to Fresnel’s coefficients and the conservation of energy flux at the interface. The unique case of reflection by metals is also analyzed. Finally, the chapter introduces birefringence, where the refractive index depends on light polarization, and presents the principles of the Fabry–Pérot resonator, an optical cavity that utilizes multiple reflections to achieve wavelength-selective transmission, with applications in spectroscopy and lasers.