Plastic materials and products are comprised of a variety of ingredients to obtain desired properties and required performance. It is important that each critical ingredient; polymers, process aids, stabilizers, and fillers, be present in the expected concentration. Objective analytical methods can be used to verify conformance for quality control purposes. Occasionally, it may be suspected that a company’s formulation has been copied, illegally, and is being made available for sale. Very detailed analysis of complex compositions can be performed with modern instrumental methods of analysis to evaluate this suspicion. And, from time to time, an unexpected and undesirable ingredient (contamination) may be found in a polymeric material. In this case, the analytical strategy is designed to provide chemical identification of the foreign material so that its source can be pin-pointed. This presentation will describe relevant analytical methods with three specific examples: an engineering resin useful in the automotive and construction industry, a medical-grade elastomer, and a specialty UV-curable coating.