The central objectives of organic farming are reducing external inputs and increasing long-term sustainability. Whilst there may be local improvements in resource efficiency, the extent to which organic livestock systems contribute to net greenhouse gas mitigation and fossil energy efficiency gains depends on the livestock type, the unit of comparison and the system boundaries in time and space. This chapter explores these factors and gives examples of where organic systems could be improved. It also considers soil carbon sequestration in organic livestock systems. Three individual case studies are presented to show how organic producers are implementing measures to improve environmental efficiency in practice. Challenges and opportunities for the sector are discussed from research, farm practice and regulatory perspectives.