With the decrease in sequencing cost and the rise of companies providing sequencing services, it is likely that personalized whole-genome sequencing will eventually become an instrument of common medical practice. We write this series of three reviews to help non-geneticist clinicians get ready for the major breakthroughs that are likely to occur in the coming years in the fast-moving field of personalized medicine. This first paper focuses on the fundamental concepts of molecular genetics. We review how recombination occurs during meiosis, how genetic variations including single nucleotide polymorphisms (SNPs), insertions and deletions are generated and how they are inherited from one generation to the next. We detail how genetic variants can impact protein expression and function, and summarize the main characteristics of the human genome. We also explain how the achievements of the Human Genome Project, the HapMap Project, and more recently, the 1000 Genomes Project, have boosted the identification of genetic variants contributing to common diseases in human populations. The second and third papers will focus on genetic epidemiology and clinical applications in personalized medicine.