The herringbone parlour, a mechanical milking technology, was invented in 1908, but took over 70 years to be adopted by the majority of British farmers. Among the reasons were the need to improve original designs, the need for complementary institutional changes such as management systems, new labour contracts and suitable herd sizes. These determinants are analysed by means comparison of regions in Britain, which also brings out roles for farmer age, capital constraints, resistance to change, and path dependence. A critical factor was the ability of regions which were late adopters to avoid investment in intermediate systems and to leap-frog the leaders. The paper concludes with a theoretical model of the innovation process.