Farm diversification presents important development opportunities and challenges in peri-urban landscapes. New economic activities in left over farm buildings have traditionally been seen as a way to broaden the income base in particular in more remote areas. The positive economic effects needs to be balanced with the negative effects of the hidden urbanization that may convert rural areas to de facto urban areas and an inefficient use of demarcated industrial zones. Nowhere is the range of interests and competition for land greater than in peri-urban areas, which therefore represent special planning challenges. We investigated the patterns and processes of On-farm Business Structure Diversification (OFBSD) in Greater Copenhagen, with a particular focus on the use of three resources: land, buildings and rural assets for OFBSD activities as well as the motives behind farm purchase. The results are based on a case study with 146 farm owners. They show that 60% of all land owners were involved in OFBSD activities. No significant relationship with particular farm or farmer characteristics was detected. An estimation of resource use indicates that buildings are essential for 95% of the OFBSD activities, while 47% and 31% of the activities rely on the use of outdoor space or nearby rural assets. The results indicate that most activities are “footloose” and might as well be located in an urban setting. Furthermore, the results indicate that many farm owners purchased their farm based on a range of motives, combining both private and business considerations. This result has important planning implications, as physical planning regulation traditionally has focused on separate domains of interest, which corresponds poorly with current dynamics of OFBSD activities in peri-urban areas.