In the last ten years, participation has become central to the social development sectors of official development assistance – smallholder agriculture, community forestry, health care, education, urban sanitation, small-scale water supplies, etc. More recently, attention has turned to the question of mainstreaming participation within the economic infrastructure sectors – transport, communications, energy, mining, construction and large-scale industry. Surprisingly, these continue to account for a sizeable proportion of oda. More significantly, perhaps, the growth in joint public/private ventures is opening new opportunities for aid agencies to influence public participation within such projects. The purpose of this Briefing Paper is two-fold: to summarise the driving forces behind this trend, and to describe the characteristics of the available operational models.