Carbon nanotubes are undoubted one of the most interesting materials in the last twenty years. The outstanding properties that these materials possess have opened a new interesting research area in nanoscience and nanotechnology, in addition, new properties have been found and possible applications are suggested for these materials frequently. Nowadays the research in nanotubes covers different fields focus to understand and applied the interesting properties of these nanomaterials, and other part have been directed to basic science with the target to modify structure and surface of carbon nanotubes. This later has allowed diversify their properties and possible uses, opening new possibilities in chemistry, physics, engineering, medicine and materials science. One of the most mentioned applications for these carbon materials is their incorporation as reinforcement in polymer matrices in order to produce new nanocomposites, taking advantage of the amazing structural, mechanical, electrical, chemical and thermal properties that carbon nanotube possess. In this context carbon nanotube nanocomposites have been developed by different research groups with the aim to produce new ultra-strong and light materials, in addition electrical conductivity and thermal properties have been studied for this kind of nanocomposites. Nevertheless, a new challenge that allows making a new age of multifunctional composite materials with these nanometric forms is starting and therefore the study of new properties in these nanocomposites is increasing significantly by scientific groups in the last five years. In this chapter we present different results of mechanical, thermal and electrical properties in carbon nanotube polymer composites, with special emphasis in novel anisotropic tribological and conductive properties that have been found recently in these nanocomposites. Chemical functionalization with focus to improve compatibility between these nanoforms and polymers is also discussed. In addition are presented the results obtained with polymer nanocomposites developments with modified nanotubes. The relevance of understand the behavior on the interface between nanotubes and polymer matrices to control and improve different properties and this way reach outstanding and novel multifunctional applications with