In vivo gene therapy is a methodological approach within the field of molecular medicine focused on the direct introduction of genetic material into the cells of a living organism to treat or prevent disease. This concept investigates the delivery and expression of functional genes, regulatory RNA, or gene-editing components *in situ* to correct genetic defects, provide therapeutic proteins, or modulate cellular pathways. Its significance lies in its potential to address the root causes of genetic and acquired diseases by modifying cellular function within the patient's body, representing a transformative strategy in biomedical therapy.