Simple Summary: Simple Summary: During the ethanol creation process, ethanol and ethanol co-products are created. Ethanol plants take these co-products and market them in a secondary market. While originally just additional revenue streams, coproducts have evolved into valuable commodities themselves. Analyzing existing research, the study finds that most of the current economic understanding is for distillers' grains, a common coproduct used in animal feed. Newer coproducts like pelletized or high-protein grains are less studied. Moreover, alternative uses for coproducts such as plastics and CO2 have remained largely unexplored. The research underscores the need for further investigation to optimize coproduct utilization and inform future decision-making. We suggest focusing on the economic pricing, marketing, and regulatory structure of newer ethanol co-products to add additional value to the ethanol industry. During the mid-2000s to the early 2010s, the domestic ethanol industry witnessed substantial growth, with ethanol coproducts emerging as vital elements for plant profitability and livestock feeding. Initially serving as supplementary revenue streams, coproducts from ethanol production have evolved into diverse value-added offerings, bolstering revenue streams, and sustaining profit margins. This study reviews existing economic research on ethanol coproducts, detailing methodologies, product focus, and research locations. Initially gathering 972 articles from 9 databases, 110 articles were synthesized. We find that most studies primarily examined the growth and future of the ethanol industry with a limited focus on specific coproducts. Feed-use distillers' grains, especially dried distillers' grains, were the most widely published while newer coproducts like pelletized, de-oiled, and high-protein distillers' grains were relatively understudied. Non-feed-use products were notably overlooked, highlighting the need for exploration beyond conventional applications. The evolving market landscape for ethanol co-products has surpassed published academic understanding of the economic tradeoffs necessitating further research into product dynamics, pricing, marketing, market structures, and regulatory frameworks. This highlights and underscores the importance of investigating value-added grains across diverse commodities and geographic contexts to inform strategic decision-making and policy formulation. [ABSTRACT FROM AUTHOR]