Current DNA binding drugs are not sequence specific. Triplex-forming oligonucleotides will bind targeted duplex DNA sites in a sequence-specific manner. A new class of DNA binding molecules based on triple-helical DNA formation promises a sequence-specific method of targeting discrete regions of DNA. DNA modifying molecules linked to third strands have been shown to modify only regions of DNA to which they were targeted. Current research will increase the understanding of triplex DNA structure and will lead to improved DNA binding drugs.