There is a general assumption about the positive effect of transparency on accountability. Even if, in theory, that link seems to be obvious, in practice the relationship is not always straightforward. Accountability and transparency can take different forms, and the relationship between them depends on the extent to which they are designed to support each other. Empirical studies show that, in some cases, transparency is a pre-condition of accountability. In other cases, transparency requirements can make accountability confusing and difficult to achieve. To be aware of the different types of accountability and transparency and how they can relate to each other is a first step towards more efficient accountability and transparency mechanisms.