New instruments and techniques have made it possible to study particle morphology and composition to an extent not previously possible. The particulates in exhaust emissions and the particles resulting from engine wear are the two examples discussed in this presentation.In order to identify physical and chemical characteristics of diesel engine exhaust particulates, specialized sampling and analytical methods are required. Some of the techniques and instrumentation are presented along with typical results of exhaust particulate analysis.The particles of wear contained in engine lubricating oil provide information about wear mechanisms by utilizing new methods of analysis. The preparation of samples and the use of ferrography and scanning electron microscopy to analyze particle characteristics are illustrated as specific examples of wear analysis.This lecture is based on the work of Dr. John H. Johnson and several graduate students at Michigan Technological University. Their work and help is gratefully acknowledged.