This work proposes a novel approach for automatic verification and synthesis of infinite-state reactive programs with respect to CTL* specifications, based on translation to Existential Horn Clauses (EHCs). CTL* is a powerful temporal logic, which subsumes the temporal logics LTL and CTL, both widely used in specification, verification, and synthesis of complex systems. EHCs with its solver E-HSF, is an extension of Constrained Horn Clauses, which includes existential quantification as well as the power of handling well-foundedness. We develop the translation system Trans, which, given a verification problem consisting of a program P and a specification φ, builds a set of EHCs which is satisfiable iff P satisfies φ. We also develop a synthesis algorithm that, given a program with holes in conditions and assignments, fills the holes so that the synthesized program satisfies the given CTL* specification. We prove that our verification and synthesis algorithms are both sound and relative complete. Finally, we present case studies to demonstrate the applicability of our algorithms for CTL* verification and synthesis   Advisor: Prof. Orna Grimberg