Despite advancements in cochlear implantation (CI) technology over the last 40 years, postimplantation performance variability remains a challenge. The electric acoustic stimulation (EAS) system is now a standard treatment option for patients with residual hearing who require CI. Genetic disorders are the leading cause of congenital/early-onset sensorineural hearing loss and also contribute significantly to late-onset hearing loss. Over the past two decades, significant progress has been made in identifying the genes responsible for deafness. Currently, over 150 genes are linked to non-syndromic hearing loss. Patients with various deafness gene mutations have shown satisfactory auditory performance after CI/EAS, indicating that identifying the genetic background can predict post-CI/EAS performance. When the intra-cochlear etiology is linked to a specific genetic background, there is a potential for improved CI performance. Identifying the responsible genes is crucial for determining the affected cochlea region. This chapter summarizes the genetic background of patients receiving CI/EAS and provides detailed clinical data and outcomes in representative examples.