This is the first major review of the developments in clinical laboratory science in the 20th century presented in the words of the original inventors and discoverers. Introductory comments by the editor help place the works within the historical context. Landmark Papers addresses: *The origin of the home pregnancy test available today in every drugstore *The woman who invented a billion dollar technology, refused to patent it and went on to win a Nobel Prize *The scientists who worked on the US Government’s crash program at the start of WWII to find a substitute for the malaria drug quinine *The blood test used to monitor the effectiveness of cholesterol lowering drugs that today are taken by over 20 million patients *The graduate student who invented a technology for testing for infectious diseases, took it to Africa to screen people for malaria for the first time and which is now used to test for HIV infection world-wide *The invention of molecular diagnostics by Linus Pauling and the road to individualized medicine *The development of the glucose meter used by diabetics up to six times a day to monitor their metabolic control