It is an important problem in the theory of modular forms to determine the structure of rings of modular forms, that is, to find explicit generators and their relations. In this talk, I will introduce the modular Jacobian approach to construct and classify the arithmetic groups acting on type IV symmetric domains, for which the rings of modular forms are freely generated. Using this unified approach, we have recovered almost all known polynomial rings of orthogonal modular forms in the literature, and found many new examples. I will also introduce the extension of this method to modular forms on complex balls and modular forms with poles on hyperplane arrangements. This talk is based on joint work with Brandon Williams.