Molecular electronic devices that utilize single molecules or molecular monolayers as active electronic components represent a promising approach in the ongoing miniaturization and integration of electronic devices. Rapid advances in technology have enabled us to engineer molecular electronic devices with diverse functionalities. Significant progress has been made in understanding charge transport in molecular systems at the single-molecule level, and concomitantly, new device concepts have emerged. This review article focuses on experimental aspects of electronic devices made with single molecules or molecular monolayers, with a primary focus on the characterization and manipulation of charge transport. (c) 2013 Elsevier B.V. All rights reserved.