This paper sets out the motivation for carrying out an observational experiment on the atmospheric boundary layer along the monsoon trough, in the light of earlier studies of the atmospheric boundary layer in India and elsewhere, and the significant role that the trough has been shown to play as a key semi-permanent feature of the southwest monsoon. The scientific objectives of the experiment are set out. and its planning and execution are touched upon. Some of the gains resulting from the experiment are mentioned, and lessons for the future about the conduct of such programmes are drawn.