Add to ORKGThis chapter reviews the recent advances taking place in the field of polymer based electrochemical sensors, in particular nanoelectrode ensembles (NEEs). In these sensors the polymer plays a crucial role in determining the specific characteristics and analytical performances. Synthetic approaches as well as principles of functioning and specific advantages and limits of NEEs are critically discussed. Useful examples of application to determinations of trace and ultratrace concentrations of inorganic and organic electroactive molecules of interest for environmental and biomedical analysis are given along with prospects in the future development of polymer based electrochemical sensors