Digital holography is a counterpart of optical holography except that a CCD/CMOS image sensor instead of the photographic films is used for recording the interference fringes, and thus can be numerical reconstruction of the three-dimensional object. Thus, the information contents, including the amplitude and the phase of holograms can be measured, stored, transmitted, manipulated and applied in digital form. Also, digital holography share the potential advantages of the parallelism and information processing capability of optics and construct a common platform between digital electronics and optics communities in terms of signal processing viewpoint. So, the main intent of our work entitled “Studies on Electro-Optical Signal Processing of Digital Holography and Their Applications” launches into new research, which focus on the theoretical investigation, image reconstruction, image processing, information encryption/decryption related applications. This study is a executed by methodology, computer simulation, experiments, hardware implementation and their applications. In addition to the study of different image reconstruction approaches, holograms can be digitally applied to various image processing such as the 3D image reconstruction of bit-plane, quantization and recognition. Finally, this work describes a full phase encoding technique for digital holographic encryption based on liquid crystal spatial light modulators, which are operated in the phase modulation mode to perform the phase-encoding object and the double random phase key masks for optical Fresnel encryption. The proposed encryption system with electrically addressed spatial light modulators provides the flexibility of the key mask design by on-line processing. This study attempted to incorporate the optical and digital techniques into an electro-optical configuration and construct a digital holographic information system with reducing storage capacity and fast transmission. Due to the superior performance of the digital holography, many potential applications will be created and realized in the near future study.