Agricultural production systems in North America have become increasingly specialized in the past few decades. Approximately two thirds of U.S. farms produce only one or two commodities, with a trend toward larger farm size. The lack of diversification has economic, biological, and environmental consequences. An alternative system, which has a historical basis in the USA, diversifies agricultural production by integrating row crop production with ruminant livestock (i.e. forage-based) production. Strategies for achieving such integration include: rotation of annual grain crops and perennial forages for grazing or conserved feed, use of relay-cropping, double-cropping, and winter cover crops to produce forage for harvest or grazing within grain crop rotations, and annual forages grown in rotation with grain crops. There are many obstacles that may prevent adoption of diversified systems, such as certain tax codes and government farm programs that favor non-diversification, economies of scale for controlling production costs that drive producers toward specialization, lack of training and negative attitudes among producers toward managing complex systems, the perception among grain farmers that forage/livestock enterprises lack profit potential on high-value cropland, and, lastly, the inherent variation in seasonal climate patterns which offers challenges to integrating forage/grazing systems with grain production. While published research is available that can address components of crop-livestock systems in humid-cool environments, there remains a dearth of published research and lack of funding opportunities for to address environment-plant-animal-economic interactions within the context of fully integrated crop-livestock systems. We will review the literature addressing specific components of integrated systems in the humid, cool-regions of North America. We will highlight current research and farmer experience with grain-livestock integration, and outline research needs related to development of diversified crop-livestock production systems that are profitable and environmentally sound.