The definition of a part time farm varies from country to country. It may be in terms of the proportion of working hours, or of income from off farm activities, or of a minimum number of hours worked on the farm. Allowing for these differences, trends in part time farming in approximately 1970-82 are compared in 10 Western European countries and 1980-82 figures are broken down by four size classes of farm (1-10 ha to over 50 ha). The absolute number of part time farms is decreasing in some cases and increasing in others. In all cases it is a rising proportion of total farm numbers. Contrary to previous belief, part time farming can no longer be considered as a transitional phenomenon. It is important both in improving the economic situation of the individual farm family and in helping maintain viable rural communities. The main danger to its future is the provision of adequate off farm employment opportunities in rural areas.