Vaucanson is an open source C++ platform dedicated to the computation with finite weighted automata. It is generic: it allows to write algorithms that apply on a wide set of mathematical objects. Initiated ten years ago, several shortcomings were discovered along the years, especially problems related to code complexity and obfuscation as well as performance issues. This paper presents the concepts underlying \Vaucanson 2, a complete rewrite of the platform that addresses these issues.