The FBI laboratory, first called the 'Criminological Laboratory,' was established in 1932, largely due to J. Edgar Hoover's commitment to applying scientific principles to criminal investigations. Since that time, laboratory personnel have been recruited from such specialized fields as geology, metallurgy, mechanical engineering, mathematics, and other physical and biological sciences and given on-the-job training in the law enforcement aspects of their specialties. The laboratory is divided into sections and units. The Document Section deals with scientific examinations of physical evidence and maintains reference files for use in conducting examinations. The Scientific Analysis Section consists of several units which handle a variety of highly specialized examinations which involve chemistry, toxicology, firearms, toolmarks, hairs and fibers, blood, metallurgy, petrography, number restoration, glass fractures, and spectrography. The Engineering Section consists of units which design and develop new radio communications equipment for use in the field, set up and maintain a network of radio stations for use in an emergency, and serve in a consulting capacity in a large number of other matters relating to radio communications. Also described are the Special Projects Section and the laboratory's reference collections. Brief case histories are provided as examples of how various units of the laboratory have helped convict the guilty and clear the innocent.