This thesis is concerned with modeling of electroabsorption modulators. Electroabsorption modulators are expected to play an important role both in the coming 40-Gbit/s optical communication systems and in next-generation, all-optical communication systems. Understanding the dynamics in electroabsorption modulators will help to support the development of high-såpeed components tailored for specific functionalities. We present modeling of all-optical functionalities realized with electroabsorption modulators. Using a model that includes propagation equations, a detiled gain model and a phenomenological model for the carrier sweep-out dynamics, we investigate all-optical wavelength conversion, all-optical signal regeneration, and all-optical demultiplexing. A detailed drift-diffusion type model for the sweerp-out of photo-excited carriers in electroabsorption modulators is presented. We use the model to calclulate absorption spectra and steady-state carrier distributions in different modulator structures. This allows us to investigate a number of important properties of electroabsorption modulators, such as the electroabsorption effect and th saturation properties. We also investigate the influence that carrier recapture has on the device properties, and we discuss the recapture process on a more fundamental level. The model is also used to investigate in detail the carrier sweep-out process in electroabsorption modulators. We investigate how the intrinsic-region width, the separate-confinement heterobarrier design, the optical power level, the number of wells and other important design- and external parameters affect the dynamical properties. We characterize the field change across the wells in a multi-quantum-well structure, and we investigate the sweep-out in a structure with shallow wells. Sweep-out upon excitation with highly energetic pulses is investigated, and the influence of carrier recapture on the sweep-out process is modeled and discussed. From our results we draw a number of conclusions concerning the carrier sweep-out dynamics in electroabsorption modulators, and about the influence that the epitaxial structure design has on the intrinsic dynamical properties.