Cloud and IT service providers should act as responsible stewards for the data of their customers and users. However the current absence of accountability frameworks for distributed IT services makes it difficult for users to understand, influence and determine how their service providers honour their obligations.A4Cloud will create solutions to support users in deciding and tracking how their data is used by cloud service providers. By combining methods of risk analysis, policy enforcement, monitoring and compliance auditing with tailored IT mechanisms for security, assurance and redress, A4Cloud aims to extend accountability across entire cloud service value chains, covering personal and business sensitive information in the cloud.A4Cloud solutions will support service providers in preventing breaches of trust by using audited policy enforcement techniques, assessing the potential impact of policy violations, detecting violations, managing incidents and obtaining redress.A4Cloud aims to improve the acceptability of cloud-based infrastructures where critical data is perceived to be at risk. It will develop techniques for improved trustworthiness of cloud ecosystems as prerequisite for accountability. Therefore it will create policies and tools that enforce responsibilities while striking a balance between transparency and privacy, and determine issues and constraints for regulators, corporate and institutional service providers, users, and their end-users.A4Cloud will have a lasting impact on the competitiveness of the European ICT sector by addressing major perceived barriers to trustworthy cloud-based services. These include concerns about complexity and enforceability of legal, regulatory and contractual provisions, socio-economic and corporate constraints, issues of trust for service-users such as risk-mitigation, privacy, confidentiality and transparency, and operational challenges such as interoperability and enforcing and monitoring compliance.