Contribution of beef and dairy cattle production in the United States (U.S.) to anthropogenic climate change is a growing public policy concern. In recent years, research in this area has begun to quantify greenhouse gas (GHG) emission sources from beef and dairy cattle production systems and develop initial mitigation strategies to reduce GHG emissions without compromising animal productivity. Developing an in-depth and accurate understanding of GHG emission sources from these cattle systems is challenging because of the variability across farms, ranches, and feedlots, and the variation between animal types on individual operations. Emission sources can be distinguished into two main categories: enteric fermentation and manure. However, to fully quantify all GHG emission sources from the beef and dairy production systems, a Life Cycle Assessment (LCA) should be completed that includes all emission sources from cradle to fork. Included in this assessment would be GHG sources associated with animal management, emissions during processing, and emissions associated with transportation of the finished product to the consumer. This chapter focuses on GHG emissions from the dairy and beef production systems derived from enteric fermentation and manure.