The objectives of this thesis were: 1) To describe and compare farm characteristics and management practices on conventional, grazing and organic dairy farms in Wisconsin; 2) To determine key factors associated to farm profitability on conventional, grazing and organic dairy farms in Wisconsin; 3) To compare conventional, grazing and organic dairy farms in terms of simulated greenhouse gas emission in Wisconsin using survey data and the Integrated Farm System Model. A comprehensive survey questionnaire was developed to collect information on farm management in Wisconsin in 2010. A total of 28 conventional farms, 28 grazing farms, and 58 organic farms were surveyed. Results indicated that farm characteristics and farm management practices were different among the 3 management systems studied. Main differences in management practices were observed in regard to feeding. Conventional farms were more likely to use rBST or feed additives such as or Monensin, were feeding a larger amount of feed and relied more on a nutritionist. Despite all those differences between the 3 management systems, a large variation was also observed inside each group, indicating that other factors than just the management system could be used to classify farms in a more homogeneous way. Variables associated to farm profitability were different among the 3 management systems studied demonstrating the importance of taking into account the specificity of the farm when trying to understand profitability. Overall simulated GHG emissions were lower on the organic and grazing farms compared to the conventional farm when expressed in CO2eq per unit of milk produced. Simulation realized with the IFSM showed that for each system, mitigation strategies were possible in order to reduce GHG emissions. Those strategies include the incorporation of grazing for the lactating cows on the conventional farms and decreasing the forage to concentrate ratio on the organic and grazing farms. For the 3 systems, the addition of a 12-mo covered manure storage and the incorporation of manure the same day of application was also an effective way to reduce GHG emission. This project resulted in the gathering of a lot of valuable information from Wisconsin dairy farms.