Carbon materials are important for many electrochemical applications due to their tunable electron-transfer and charge-storage properties. Judicious structural manipulation of carbon to modulate its chemical, electronic, and crystalline properties is key to the rational design of many high-performance electrochemical devices. Here we focus on three types of carbon nanomaterials of recent interest in electrochemistry, namely, carbon nanofibers, carbon nanotubes, and graphene. We concentrate on how structural variations in these carbon nanomaterials impact their electrochemical activities. In this review, following a brief overview of the synthesis methods for each class of carbon nanomaterials, we discuss their electrochemical applications for sensing, electrocatalysis, and energy storage, with emphasis on general carbon structure manipulation strategies that impart specific functionalities to suit each application area. Special attention is devoted to articulating how the electronic structure of carbon influences its electrochemical activity. Through the analysis of different electrochemical devices, we find that some of the modification techniques apply to more than one application area; thus structural manipulation methods in one class of electrochemical devices may be extended to other types. (C) 2014 Elsevier Ltd. All rights reserved.