The 2017 Nobel Prize in physiology or medicine was awarded to three scientists from the United States, Jeffrey C. Hall, Michael Rosbash, and Michael W. Young, for their discoveries of genes and molecular mechanisms of the biological clock of fruit flies. The biological clock, also called circadian rhythm, is any biological process that oscillates with a period of about 24 hours. It is a common and basic phenomenon of lives in nature. The discoveries of clock genes and the elucidation of the molecular mechanisms of the clock shed lights on the understanding of the nature of life, particularly the relationships among genes, behaviors, and environments, and provide the bases for applications of the principles of the biological clock in our life.