The present invention relates to delivery of biologically active molecules to cells. Specifically, the invention relates to polycationic compositions, polymers and methods for delivering nucleic acids, polynucleotides, and oligonucleotides such RNA, DNA and analogs thereof, including short interfering RNA (siRNA), ribozymes, and antisense, or peptides, polypeptides, proteins, antibodies, hormones and small molecules, to cells by facilitating transport across cellular membranes epithelial tissues and endothelial tissues. The compositions and methods of the invention are useful in therapeutic, research, and diagnostic applications that rely upon the efficient transfer of biologically active molecules into cells, tissues, and organs.