Due to its importance in animal feed, soybean meal has been extensively studied to optimize its use in livestock diets. Despite extensive research, the industry has not fully characterized specific areas of soybean processing such as the inclusion of soybean by-products added back to soybean meal during processing. Soybean processing by-products can encompass a large variety of materials including weeds and foreign material, soybean hulls, gums, soapstocks, lecithins, spent bleaching clays, and deodorizer distillates. Despite the potential for being added back to soybean meal when a crushing plant is integrated with an oil refinery, there is currently limited information on the composition of many of these soybean processing by-products and their subsequent effects on soybean meal quality and animal performance. Therefore, there may be opportunities for a new area of research focused on soybean processing by-products and their optimal use within the livestock feed industry. This review summarizes the current information on soybean by-products with a focus on identifying the areas with the greatest potential for future research in swine and poultry nutrition.