This paper explores the development and automatization of DNA sequencing leading to a generation of physical and genetic maps by the well-discussed Human Genome Project (HGP). This led to the accumulation of a wealth of knowledge about the genetics per se and its possible variations, and it took no time to find the links between complex diseases and practice of medicine, although it is still challenging to integrate genetics into the everyday practice of clinical medicine. Sufficient advances have been made to date in the area of understanding disease etiology and pathogenesis from the perspective and context of genetic variation as a driver, and with development of modern genetic laboratory technologies, it is now a reality that in the near future, there would be increasing role for genetics in the diagnosis, prevention, and treatment of complex diseases, almost all except those caused by trauma. In fact following the knowledge accumulation from the Human Genome Project, the causation of common and complex diseases in relation to genetic variation in the fields of molecular epidemiology, medicine, and pharmacogenomics was a prime research interest. This was in sharp contrast with the traditional approach of studying human diseases contemplated to be caused by relatively rare single-gene diseases, which cumulatively account for merely 10% of diseases appear in the pediatric age group. However, in reality, the post-Human Genome Project research in this field is tending to increasingly demonstrate that virtually every medical condition has a genetic component. There is, however, considerable difficulty in characterizing these conditions since there is a vast number of genetic variations and their combinations, synergistic effects of multiple causative genes, and reactions of genetic traits with environmental factors, all of which may play roles together to cause manifestations of a complex disease.