We have reported the catalyst-assisted hot-filament chemical vapor deposition (HFCVD) of various carbon nanostructures, such as carbon nanotube (CNT), nanoparticle (CNP), and nanofiber (CNF), and their application examples. In the case of CNT, vertically aligned high-density growth has been investigated in detail using in-situ optical reflectivity measurement. For CNF showing large field-emission currents, adsorbate-related emission behavior and the emission from patterned cathodes have been studied. Regarding CNP, the performances of a series of triode field emitters with CNP cathodes have been compared, and the application of CNF triode to miniature time-of-flight mass spectrometer has been discussed. (c) 2007 Elsevier B.V. All rights reserved.