The report describes the use of receptor models to determine the source contributions to ambient particulate matter loadings at sampling sites, based on common properties between sources and receptors. (This is in contrast to using source models which start with emission rates and meteorological measurements to predict ambient concentrations). Three generic receptor models have been identified: chemical mass balance, multivariate, and microscopial identification. Each has certain requirements for input data to provide a specific output. An approach that combined receptor and source models, source/receptor model hybridization, has also been proposed, but it needs further study. The input to receptor models is obtained from ambient sampling, source sampling, and sample analysis. The design of the experiment is important in obtaining the most information for the least cost. Sampling schedule, sample duration, and particle sizing are part of the ambient sampling design. Analysis for elements, ions, carbon, and organic and inorganic compounds is included in the sample analysis design. Which sources to sample and how to sample them are part of the source sampling design.