This chapter presents its content in a list-based format, focusing on key concepts related to thermodynamics, aerodynamics, stage design, curve profiles, performance maps, and specific speed as they pertain to centrifugal compressorCentrifugal compressor impellers. These topics are supported by illustrative figures to aid in the explanation and comprehension of fundamental principles. While quantitative data such as typical ranges and values for impeller aerodynamicImpelleraerodynamics design can be found extensively in existing literature, this chapter opts for a qualitative approach to the subject matter. Additionally, it offers a detailed overview of how inlet conditionInlet condition effects variations, surge and stonewall phenomena, impeller manufacturing techniquesImpellerfabrication methods, standard materials, material selection criteria, and operational stresses influence overall compressor performance.