This is a study of efforts to improve the responsiveness of public service providers to the needs of service users, particularly the poorest service users. This paper examines over sixty case studies of both public-sector reforms to foster stronger client focus in service delivery; and civil-society initiatives to demand improved services. This work was concerned to identify means of amplifying citizen 'voice' such that engagement with the state moves beyond consultative processes to more direct forms of influence over policy and spending decisions. The case studies upon which this research is based are drawn from around the world, from developing and developed countries. They are organised into 14 different types of 'voice' or 'responsiveness' mechanisms, and are available on: www.ids.ac.uk/ids/govern/ citizenvoice/annexcs.html. Across different types of public service, the potential for citizen voice, and varying degrees of public sector responsiveness, can be surmised from features of service design and delivery such as the complexity of the technology involved in the service, the remoteness, geographical, social and educational, of providers, the extent to which the service is a shared good or an individually consumable product, or the social and environmental consequences of dramatic service break-down. Variations in voice and client focus are also explained by client characteristics: the social status of clients, their geographic concentration, and whether they have a sustained or one-off relationship with providers. The study concludes with policy-relevant findings on ways of enhancing citizen voice in decision-making, planning, and monitoring of public services. For citizen engagement with public service providers to move beyond consultation to real influence, citizens must enjoy rights to a more meaningful form of participation. This would include formal recognition for citizens' groups, their right to information about government decision-making and spending patterns, and rights to seek redress for poor-quality service delivery. Public sector providers, for their part, need assurances regarding the mandate and internal accountability of such groups. This study was commissioned by the UK's Department for International Development (DFID).