Advancements in the micro/nano-fabrication techniques have opened up new avenues for the development of portable and easier-to-use biosensors. Over the last few years, carbon electrodes have been widely used as sensing units in biosensors due to their attractive physiochemical properties. This book details different strategies to develop functionalized high surface carbon micro/nano-electrodes for electrochemical and biosensing devices. Carbon electrodes were fabricated via carbon-MEMS technique, which is based on pyrolyzing prepatterned photoresist. To increase the surface area of the carbon electrodes, multiple approaches such as (i) fabrication of porous 3D carbon microarrays, (ii) conformal coating of graphene onto 3D carbon microarrays, and (iii) fabrication of controllable carbon nanostructures were investigated. For carbon surface functionalization to covalently attach biomolecules, different oxidation techniques and the resultant surface carbon–oxygen groups were analyzed and compared. Lastly, label-free detection of platelet-derived growth factor oncoprotein, a cancer biomarker, was demonstrated on 3D carbon microarrays platform with sub-nanomolar detection limit.