I now endeavour, through selected case material from Mexico, to show the usefulness of the idea of interface for depicting organising practices and processes of knowledge/power construction.1 I first concentrate on rural development situations, using data collected in the late 1980s and early 1990s. This is then followed by a recent study of street children in Mexico City which utilises an interface perspective to explore the contradictory dynamics of interventions designed to get them off the streets.