In this chapter, we provide a general overview of how cochlear implants work, design considerations for cochlear implant signal processing, primary constraints and limitations, as well as contemporary efforts aimed at mitigating these limitations. We discuss spectral and temporal coding of sound by CI speech processors, as well as factors such as current spread and auditory-nerve health that limit the transmission of spectral and temporal features of sound. Finally, we discuss hearing preservation and signal processing for bilateral CIs, two areas that are receiving increasing attention in the field.