The aim of this book is to take stock of the experiences of Spain and Portugal in the adaptation to the IPSAS, showing the advantages, disadvantages and the main challenges for its implementation. In chapter one, the book analyses the IPSAS and the conceptual framework, as well as the claimed benefits and criticisms of IPSAS. Chapter two makes an analysis of the diffusion of the IPSAS in the international framework and the process of harmonization in development in Europe. Chapter three and four analyze the process of adaptation to IPSAS in Portugal and Spain respectively. In the chapter five, there is a comparative analysis between Spain and Portugal, and the last chapter present the main conclusions. This book can help to understand the level of implementation of the reforms and how governments are applying the IPSAS.