The analysis of sports samples for prohibited substances began in the 1960s and has developed since then using modern technologies close to the latest scientific discoveries. In this chapter the latest techniques and applications are described as well as the role of the World Anti-Doping Agency as the controlling body for the implementation of these tests. For small molecules, apart from the routine use of GC-MS, the newer techniques include the use of isotope ratio MS to detect testosterone and nandrolone administration and LC-MS/MS (liquid chromatography-tandem MS) to detect diuretics. For large molecules, several applications of LC-MS/MS are described as well as immunoprocedures for erythropoietin and human growth hormone. Finally, the latest method to detect homologous blood transfusion is briefly described.