iProver -- an instantiation-based theorem prover for first-order logic. iProver is an instantiation-based theorem prover which is based on Inst-Gen calculus, complete for first-order logic. One of the distinctive features of iProver is a modular combination of instantiation and propositional reasoning. In particular, any state-of-the art SAT solver can be integrated into our framework. iProver incorporates state-of-the-art implementation techniques such as indexing, redundancy elimination, semantic selection and saturation algorithms. Redundancy elimination implemented in iProver include: dismatching constraints, blocking non-proper instantiations and propositional-based simplifications. In addition to instantiation, iProver implements ordered resolution calculus and a combination of instantiation and ordered resolution. In this paper we discuss the design of iProver and related implementation issues.