Since 2003, Accenture has been working with the French Tax Office on a new program to simplify and improve the relationship between the agency and the taxpayers. Along with the implementation of the personal tax account system and the TeleIR applications, the challenges were to build an online national database of 40 million taxpayers and to deliver secure access based around a PKI solution with digital signatures for electronic forms. Olivier will describe how the Accenture team ensured maximum performance through modularity and reliability of the JBoss Application Server, as well as operations performance with a JBoss implementation on more than 500 Red Hat Enterprise Linux servers. They successfully turned it into a heterogeneous mission-critical environment, mixing professional open source and closed source software components. Technological risks and time-to-market were minimized through the use of JBoss community-driven professional frameworks, such as Hibernate. JBoss worked hand-in-hand with the Accenture architecture and development team to avoid pitfalls and anticipate any potential issues before going live, leading to the major success of the 2007 income tax return campaign.