High-quality mats of single- and double-walled carbon nanotubes (SWNT, DWNT) have been grown by the catalytic chemical vapor deposition (CVD) technique. Field-emission scanning electron microscopy (FFSEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy revealed densely packed mats made by SWNTs, a small fraction of DWNTs, and bundles of both. Tube diameters range from 0.72 to 6 nm. Remarkably, Raman measurements show a very high ratio between the G-band and the D-band peak intensities, a clear indication that structural defects and amorphous carbon are largely absent, without any post-growth treatment.