Technical Abstract: Both organic and conventional dairy farming practices in the U.S. have unique challenges for maintaining sustainable production. Economic sustainability may be most important because milk will not be produced in our economy unless there is profit for the producer. The demand for organic milk has created a more stable price that is normally substantially greater than the commodity price of conventional milk. As long as this price difference is maintained, organic dairy production offers an economically viable option, particularly for smaller farms. A readily available and relatively inexpensive supply of organic fertilizer is a challenge for organic producers. In our region, poultry manure provides an organic source of crop nutrients. When applied to meet nitrogen requirements, phosphorus requirements are normally exceeded. Over time, this can lead to high soil phosphorus levels and greater phosphorus runoff in surface water. When well managed perennial grassland is used as the primary feed in organic production, soil erosion and nutrient runoff are small. Organic farms that use row crops for feed production rely heavily on the use of tillage for weed control. With greater tillage, sediment and nutrient losses can be much greater than that found with conventional no-till practices and herbicide use. Organic practices may also increase the net greenhouse gas emission from farms. This again is linked to the use of poultry manure or other organic nutrient source for plant nutrition. The additional carbon brought onto the farm builds soil organic matter, which over years leads to greater soil respiration and loss of carbon. This additional emission, along with a lower milk production per cow, can increase the carbon footprint (net emission per unit of milk produced) of organic systems. The sustainability of both organic and conventional dairy production systems varies considerably dependent upon the management practices used. Organic systems have the greater challenge since available resources and management options are more limited.