Catalysis is currently recognized as a potential field of application for carbon nanotubes, and throughout the past decade the number of publications and patents on this subject has been increasing exponentially. In most of these cases, the use of these nanomaterials as support structures facilitates better performances than conventional supports. To date, most of the research has focused on supported metal catalysts, in which the active phase is located on the external surface of the carbon nanotubes. The selective deposition of metallic nanoparticles in the inner cavity of nanotubes, which could allow the exploitation of advantageous confinement effects, has received much less attention. In this Minireview, the different strategies for the preparation of such nanocatalysts, as well as the benefits that could be expected from the resultant confinement effects are presented, with the aim of highlighting their potential use in catalysis.