An extension campaign is a coordinated effort to inform many farmers in a relatively short period of time about an agricultural topic of widespread concern or interest. The aim is to achieve quick, large-scale change in farmer behaviour and practices through carefully choreographed efforts by different organisations, using a variety of communication channels. An extension campaign requires a sharp focus (Box 1) and a clear end point. It should deliver material benefits to farmers, whose needs and demands are paramount in shaping the campaign.