Combining objects with diverse properties has often the advantage of giving rise to novel functionalities. In this scenario, metal-filled and decorated carbon nanotubes (m-CNTs) represent a class of hybrid carbon-based nanostructured materials with enormous interest for application in several fields, ranging from nanoelectronics and spintronics to nanomedicine and magnetic data recording. The present review will provide the reader with an overview of state-of-the-art hybrid architectures based on m-CNT systems, methods currently employed for their fabrication, the set of their unique properties and how they can be applied toward novel devices with multifunctional properties for a broad range of applications. (C) 2014 Elsevier Ltd. All rights reserved.