This chapter discusses the most recent developments in the fields of biosensing and electrochemical sensing employing nanoelectrode arrays (NEAs) and ensembles (NEEs), with a primary emphasis on their use in specialized diagnostics in the medical area. First, a quick overview of how NEE and NEA are made and how they are used to identify physiologically significant analytes at extremely high sensitivities. Additionally, a synopsis of the most current theoretical developments regarding the modeling of pertinent electrochemical signals is provided, followed by a brief introduction to the characteristics and potential benefits of electroanalytical signals. In addition to unique (bio)functionalization techniques, novel nanofabrication techniques and nanoelectrode materials are presented as means of achieving more dependable and sensitive sensors. The integration of NEA/NEE -based sensors with live cells and their use in neurochemical research are two examples of the advanced uses of these sensors in the biomedical and biological fields. Finally, the field’s advancements, current limitations, and future research opportunities are explored. Regarding directions for future study, it is necessary to create theoretical models that account for certain factors, such as quantum mechanical and double layer properties, that can govern electrochemistry with arrays of nanoscale electrodes. However, cutting-edge research on the use of NEA/NEE in the neurochemical and biomedical domains will be able to pave the way for new developments in both basic understanding and practical application.