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Triplex-forming oligonucleotides have been explored in the last 3 decades as highly specific gene-modifying agents. Such agents have been showed to either upregulate or shut down gene expression in vitro, an outcome that depends on the specifically designed biological system. One interesting approach is to tether to the oligonucleotide a photoreactive moiety. After hybridization to the DNA target (typically single- or double-stranded DNA), a site-specific photoinduced reaction may take place at a timely manner. Further, as the light source may be focused at a certain area, one has control on the location at which the phototriggered DNA modification takes place. In this regard, the use of tissue-penetrating photons (typically 630–950 nm) would be most relevant for in vivoapplications as photoactivation may lead to site-specific DNA modification at a specific tissue/organ. In this review we highlight the advances made in this field and discuss the hurdles that lay ahead for the realization of phototriggered triplex-forming oligonucleotides as a solid therapeutic approach. [ABSTRACT FROM AUTHOR]