On July 24, 1969, the first extraterrestrial samples, with the exception of meteorites, were returned to earth by Apollo 11. Since then these samples and the samples returned by Apollo 12 have been subjected to scientific investigations by hundreds of scientists from many countries. Drawing on advances from the last 25 years of study of meteorites and terrestrial rocks the variety and sophistication of the techniques used on these samples is truly impressive. It can truthfully be said that 10 years ago we could not have made the measurements, and that, even if we had had the data, we could not have interpreted it. The electron microprobe, the scanning electron microscope, and the mass spectrometer, as well as other instruments and techniques, have joined the microscope as routine tools with which to attack a petrologic problem.