The present invention concerns a design for dendritic poly(amino acid) polymer carriers, also known as nonlinear polymers, and their applications. These dendritic poly(amino acid) carriers have multiple functional groups at the polymer surface. In addition, they have heterofunctional groups on the poly(amino acid) side chains for drug or diagnostic agent attachment. They are designed to allow sufficient preservation of the binding affinity of the targeting ligand while conjugating therapeutic or diagnostic agents to the polymers. The present invention also describes methods of production of the polymer carriers and methods for the treatment or diagnosis of diseases employing the polymer carriers. The present invention also includes methods to introduce targeting moieties site-specifically to the end of polymer chains.