Abstract: The present invention provides specific double-stranded DNA/RNA binding compounds having a polymeric structure, which are in fact, triplex forming molecules capable of binding tightly and specifically to predetermined sequences in the major groove of double stranded nucleic acid molecules; as well as pharmaceutical compositions comprising thereof. The triplex forming molecules and the pharmaceutical compositions of the invention can be used for various therapeutic applications such as site-specific modulation of gene expression and targeting of DNA or RNA damage, as well as for diagnostic applications in vitro.