The 2021 Conference on Implantable Auditory Prostheses is the 20th in a series of biennial international research conferences on cochlear implants and auditory brainstem implants. CIAP 2021 provides a unique forum for the presentation and discussion of fundamental scientific research from a diversity of basic science disciplines, as well as input from clinicians, engineers, and technical staff. The close interaction among leading scientific researchers from around the world facilitates the exchange of up-to-the-minute research results.The CIAP meetings originated in 1983 under the auspices of the Gordon Research Conferences that sponsored the first three such meetings. Prior to the initiation of this series of Conferences, the need for such scientific exchange was met primarily through informally organized meetings entitled West Coast Cochlear Prosthesis Workshops which have since been discontinued and have been replaced by the CIAP series.. The purpose of these meetings has been to provide for close interaction among leading scientific researchers from around the world and to exchange up-to-the-minute research results.Such interaction is particularly important in this field because of its highly interdisciplinary nature and the rapid pace of technological progress. It includes fundamental scientific research in areas as diverse as auditory neurophysiology and biophysics, electrochemistry and biomaterials, adhesion chemistry, cochlear anatomy and histopathology, biomolecular techniques for tissue engineering, electrical field theory, bioengineering, neuroradiology, signal processing, psychophysics and perception, cognitive psychology, language development, speech science, developmental and molecular biology, and learning. Because it involves direct application of these pursuits to a significant clinical problem, it also requires substantial input from experts in electrical and mechanical engineering, otologic surgery, audiology, and speech-language pathology, as well as interaction with technical staff from commercial companies that ultimately produce the clinical devices.A hallmark of these meetings has been a strong focus on hard science and in-depth discussion of current technical issues. This is reflected in the meeting format, retained since the first Gordon Conference, comprising invited papers presented by speakers with expertise in their respective fields. A substantial fraction of the formal program time is allocated for discussion among all participants. The two-year interval between meetings permits significant incremental progress to be available for reporting at each meeting. Generally not included are tutorials, reviews, summaries of clinical data, or reexamination of well-established principles. Often, when progress in a non-implant-related field is considered to have significant potential benefit for cochlear implant development, experts from the new discipline are invited to present their progress and participate in the entirety of the meeting to facilitate seeding of new ideas in the implant community.The emphasis on leading-edge science differentiates this series of meetings from other cochlear implant conferences, which generally present a more clinical orientation. Conference attendance has grown steadily from approximately 50 participants in 1983 to 360 in 2009 to 450 in 2011. At every meeting participants have voiced a strong desire to reconvene at two-year intervals, and in each case a formal mandate to do so has been provided by election of a Chair and Co-Chair to be responsible for organizing the succeeding conference.