This project investigated the business, environmental and social sustainability of dairy farms that include dairy support land. Seventeen farmers were interviewed using Yin’s case study method (Yin, 2003). The interviewees were selected from a list provided during a series of focus groups done with rural professionals prior to continuing with the main body of the research. Those interviewed saw that the primary role of dairy support land is to protect the dairy farm from external factors. Dairy farms are vulnerable to externalities due to high fixed costs and the relationship between cow condition and milk production. The ability of dairy support land to manage externalities relates to quantity of feed grown, therefore feed grown is perceived as the most appropriate measure of performance. For dairy support land to be sustainable, it must be well resourced. On a fully resourced DSL unit, there will be time to plan and carry out essential tasks and environmentally important developments such as riparian fences and stockwater systems are likely to be in place. If the dairy support land unit is not fully resourced it will become a liability to the overall system as the supply of feed becomes unreliable, cows calve in poor condition and dairy farm staff and management are overextended. Poorly resourced dairy support land is also unlikely to have environmentally friendly developments in place. The case studies also demonstrated that the fundamentals of sustainability and practice remain constant across a variety of soil and climatic conditions in Canterbury and Southland.