In this chapter, we review our recent findings on the modeling and analysis of inverse problems in imaging modalities using resonant contrast agents. We start by motivating the need of using contrast agents in imaging (but also in the drugs delivery and therapy modalities at large) and highlight why their resonant effect is the key feature. We describe the close link between the contrast properties of these agents and the classes of resonances they can generate. These resonances are characterized using two related but different ways. First, as the scattering resonances (i.e. generalized eigenvalues) of the related operator. Second, as the only frequencies for which the resolvent of this operator is not trivial (does not coincide with the one of the background one, called the free operator). For those resonant frequencies, this resolvent is nothing but the one of the point-supported singular perturbations of the free operator. This point-like perturbation is given as point-source to which is attached a scattering coefficient modeling the interaction between the contrast agent and the surrounding background. In addition, this scattering coefficient reaches its maximum, as a function of the frequency, at the (dominant real part) of the resonant frequencies. As a consequence of this second characterization, these resonant contrast agents considerably amplify any incident wave (or source) sent at frequencies close to their resonances. This allows to perform quantitative estimates of the background medium using remote measurements. Following this approach, we describe recent results obtained in the frameworks of Ultrasound, Optic and Photo-Acoustic imaging.