Advances in genetics and genetic engineering have brought about a profound transformation in traditional medical concepts, shifting the focus from treating the apparent symptoms of disease to understanding their precise molecular causes at the level of genes and cells. This transformation has laid the foundations of modern precision-based and personalized medicine, leading to improved early diagnosis, the development of more effective therapies with fewer side effects, and the opening of new avenues for treating diseases that were previously considered incurable. Genetic engineering is concerned with the study of the genetic material of living organisms and its direct manipulation through advanced techniques such as recombinant DNA technology, gene cloning, and gene editing. The discovery of the structure of deoxyribonucleic acid (DNA) marked the true starting point of this field, as it enabled a deeper understanding of the relationship between genes and both normal and pathological biological functions within the human body. With the advancement of genetic analysis tools, it has become possible to identify genetic mutations responsible for many diseases with high accuracy, allowing medicine to transition into the era of molecular diagnosis. In the field of disease diagnosis, genetic engineering has played a pivotal role in the early detection of hereditary disorders and chronic diseases. For example, genetic testing is used to diagnose inherited blood disorders such as sickle cell anemia and thalassemia before the appearance of clinical symptoms, enabling preventive intervention and reducing disease-related complications. Genetic analysis has also contributed significantly to cancer diagnosis by identifying tumor-specific genetic mutations, such as mutations in the BRCA genes associated with breast and ovarian cancers, which helps clinicians assess disease risk and develop appropriate therapeutic and preventive strategies. The role of genetic engineering is not limited to diagnosis; it extends to the development of innovative therapeutic approaches, most notably gene therapy. This form of treatment is based on introducing a functional copy of a gene into a patient’s cells to compensate for a defective gene or to correct the underlying genetic abnormality. Gene therapy has achieved notable success in treating certain inherited immunodeficiency disorders, such as severe combined immunodeficiency (SCID), as well as some hereditary blood disorders. In addition, clinical trials have shown promising results in the use of gene therapy for the treatment of neurological and muscular diseases that previously lacked effective therapeutic options. Genetic engineering has also contributed to the development of targeted therapies that focus on specific molecular pathways within diseased cells. This approach represents a major breakthrough in cancer treatment, as drugs are designed to selectively target tumor cells while minimizing damage to healthy tissues, as seen in therapies used for certain types of leukemia and lung cancer. Such strategies have led to improved treatment response rates and reduced side effects compared with conventional chemotherapy. One of the most prominent applications of genetic engineering in modern medicine is personalized, or precision, medicine, which relies on an individual’s genetic profile to determine the most appropriate therapeutic plan. Studies have shown that drug responses vary among individuals due to genetic differences, prompting the use of genetic analysis to guide drug selection and dosing, particularly in the treatment of cardiovascular diseases, cancer, and psychiatric disorders. This approach enhances therapeutic efficiency and reduces the risk of adverse drug reactions. Despite these significant scientific achievements, the medical applications of genetic engineering raise several ethical and scientific challenges. Interventions in the human genome, especially those involving germline gene editing, raise concerns about their potential impact on future generations. Additional issues include the confidentiality of genetic information and the possibility of its misuse, as well as the high cost of advanced genetic technologies, which may contribute to health disparities among societies. In conclusion, genetic engineering represents one of the fundamental pillars of modern medicine, having driven a genuine revolution in disease diagnosis and treatment and opened broad prospects for more precise and humane medical practice. With continued scientific research and the development of ethical and regulatory frameworks, genetic engineering is expected to play an increasingly important role in improving human health and achieving a more advanced and sustainable medical future. Dr. Asseel Hashim Radhi