Several exact and numerical techniques have been established for solving the inverse (electromagnetic) scattering problems in connection with cylindrical bodies. As far as we know, in almost all published works it is assumed that the body is illuminated by a plane or line source excited wave while the beam illumination case, which is more important and convenient for practical applications, has not been well studied. The aim of this paper is to solve the inverse (electromagnetic) scattering problem related to cylindrical bodies buried in a half-space by considering that the incident wave is a Gaussian beam. In the derivation of the theory presented in the present paper, we utilize the plane wave spectral representation of a Gaussian beam. The results concerning the reconstruction of the geometrical properties are quite exact while what concerns the physical properties is valid under the Born approximation, which can always be met by properly adjusting the frequency of the incident beam. An illustrative example to show the advantages of using beams in the reconstruction of objects is also given.