The thesis deals with the analysis and modeling of high-impedance surfaces. High-impedance surfaces are resonant cavities synthesized by printing a periodic frequency selective surface on the top of a grounded dielectric slab. The first part of the thesis is dedicated to the modeling of high-impedance surfaces and frequency selective surfaces which constitute the key element of the HIS structures. High-impedance surfaces are then analyzed when employed in the design of low-profile antennas and ultra-thin electromagnetic absorbers. The last part of the thesis deals with the so-called Fabry-Perot antenna. The presented theoretical work is supported by several experimental demonstrations.