This chapter reviews the researches and the most relevant progresses in polyetherimide (PEI) science and provides a comprehensive source of information on history synthesis, processing and applications. The ingenious application of nitro-displacement reaction on the synthesis of polyetherimide as well the existing one step polymerization methods, the new approaches and innovative solutions in processing operations are summarized. Due to the high engineering performance of PEI material, an extensive section on mechanical, electrical, chemical and thermal properties is included. The thermo and photo oxidative behaviours, the hydrolytic stability and the the consequent modification on PEI chemical structure are also discussed. The new development of PEI materials such as blends, composites with particular attention to nano-composites, and the most recent patents and …