Distillers dried grains with solubles (DDGS) is a complex heterogeneous granular solid that exhibit a wide range of physical and chemical properties. This fact is one of the major reasons that livestock nutritionists often find it difficult to include it in their feed rations. The rapid growth of the corn ethanol industry, the primary generator of DDGS, has resulted in a huge influx of this product into the marketplace. Unfortunately, the lack of standard methods for product quality determination and reporting is becoming a bottleneck to expanding the market for this product. Challenges in the logistics of moving DDGS through the market chain, primarily via rail, is also a cause of concern. This paper discusses past and the current state of research on the physical properties of DDGS and their determination. In particular is examines the causes of variability in particle density (PD), bulk density, particle morphology (particle size and shape) and particle size distribution (PSD). It also highlights the importance of developing standards for DDGS physical characteristics, measurement methods, and reporting that will be useful for the design of handling and storage systems, as well as DDGS product trade.