A number of drug-carrier systems have been considered, so far, for time-controlled delivery, targeting, and decrease of toxicity of biologically active compounds. Many of these drug carriers are based on synthetic polymers. Prerequisites for polymeric drug carriers and the need for polyvalent systems capable of carrying different drugs are examined from the viewpoint of effective pharmaceutical uses. The cases of microcapsules, microspheres, nanoparticles, and emulsions based on polymers are recalled. Of particular interest are copolymers, such as amphiphilic block-copolymers and partially quaternized polytertiary amines, that can form hydrophobic microdomains in aqueous media. Discussions are focused on the capability of the corresponding microphases to solubilize, carry, and release lipophilic drugs. The present state of the art is illustrated by recent examples.