Semiconductor technology requires probably more sophisticated characterization tech-niques than any other modern technology. For example, many applications require atomic sensitivities of 1 ppb or less and we may be interested in analyzing a volume 10-16 cm3 (hopefully not at the same time). In addition to chemical analysis of very small volumes, determination of the chemical state (oxidation state, etc.) of the constituents is many times critical. Of equal importance, especially for the high density of devices contemplated for very large scale integration, is the detection and characterization of defects present in the wafer starting materials. In addition to the optical techniques, which are the subject of this conference, many other techniques including X-ray topography, electron beam induced current, Auger electron spectroscopy, X-ray photoelectron spectros-copy, Rutherford backscattering, and secondary ion mass spectrometry have been applied to these problems. This paper will be broken into two parts. First I will discuss some of our future needs in semiconductor characterization emphasizing requirements for sub-micron devices in silicon and potential materials problems in non-silicon technology. Next I will review the capabilities and limitations of some of the non-optical techniques mentioned above to indicate specifically where additional capabilities are necessary.