The behavior of mixtures of polymers with carbon nanotubes are reviewed. The use of polymers as dispersing agents of individual CNT is described in detail. Two groups of polymer-CNT systems are presented. One corresponds to the case in which the polymer-CNT interactions modify the electronic properties of the tubes. The second case corresponds to the polymers end-tethered to the tubes. This case results in changing the inter-tube interactions from strongly attractive to repulsive, through the entropic (steric) polymer induced repulsions. It is shown that the shape and dimensionality of the tubes determines the strength, range and type of inter-tube van der Waals attractions and polymer induced repulsions. The experimental verification of these ideas, and their implications for tube dispersions and separation are discussed. (c) 2005 Elsevier Ltd. All rights reserved.