The addition of the Si-Li detector to the electron probe, the scanning electron microscope, and more recently the transmission electron microscope (resulting in the analytical electron microscope) has made it possible to obtain elemental analysis on individual “particles” with dimensions less than 1 nm using EDS. Although some initial particle studies on micrometer-sized particles were done on the electron probe using wavelength dispersive spectrometers, WDS, the variability and complexity of many particle compositions coupled with the high currents necessary for WDS made elemental analysis of particles by WDS difficult at best. In addition, the use of multiple spectrometers, each with a different view of the particle and therefore different particle geometry as shown in Fig. 1, limited the quantitative capabilities of the technique. With the introduction of the Si-Li detector, there was only one spectrometer with a single geometry resulting in the development of various procedures for obtaining quantitative elemental analysis of the individual particles.