Recent discoveries indicate that when the materials are brought down to sizes in the range 1-100 nm, these exhibit unique electrical, optical, magnetic, chemical, and mechanical properties. Methods have now been established to obtain the monodisperse nanocrystals of various metallic and semiconducting materials, single-walled and multi-walled nanotubes of carbon and other metallic and non-metallic materials together with organic nanomaterials such as supra-molecular nanostructures, dendrimers, hybrid composites with tailored functionalities. The high surface-to-volume ratio with an added element of porosity makes these highly potential candidates for chemical and biological sensor applications with higher degree of sensitivity and selectivity as compared to their bulk counterparts. The paper reviews the recent developments and applications of chemical and biological sensors based on nanomaterials of various structural forms. © 2008, DESIDOC.