Abstract A survey is given on typical ‘top-down’ and ‘bottom-up’ approaches to design nanostructured sensors which monitor different physical and chemical quantities. Particular emphasis is put on new materials and transducers for molecular recognition by chemical sensors. These convert chemical information into electronic signals by making use of suitable ‘key-lock’ structures. This requires the control of surface structures of chemically sensitive materials down to the molecular scale under thermodynamically or kinetically controlled conditions. This in turn requires the molecular understanding of sensor mechanisms which is deduced from comparative microscopic, spectroscopic and sensor test studies on ‘prototype materials’. Selected case studies illustrate the common mechanisms of molecular recognition with electron conductors, ion conductors, mixed conductors, molecular cages, polymers and selected biomolecular function units.