In developing countries in particular, services are often delivered through unorthodox organisational arrangements that cannot simply be dismissed as relics of ‘traditional’ institutions, or as incomplete modern organisations. Some have emerged recently, and represent institutional adaptations to specific political and logistical circumstances. We need to expand the range of organisational categories that are considered worthy of study and develop a better understanding of the strengths and weaknesses of unorthodox arrangements. The concept of institutionalised co-production provides a useful point of entry. Institutionalised co-production is defined as: the provision of public services (broadly defined, to include regulation) through a regular long-term relationship between state agencies and organised groups of citizens, where both make substantial resource contributions. We explain some varieties of institutionalised co-production arrangements; explore why they appear to be relatively so widespread in poor countries; and relate the concept to broader ideas about public organisation.