The Workshop on Tool Building in Formal Methods is held in conjunction with the 2nd International ABZ Conference (ABZ 2010), Orford, Quebec, Canada, Monday 22 February 2010. Scope of the Workshop: The object of this workshop is to share ideas, methods, and processes that are used to build tools supporting formal methods. Discussions may also deal with maintenance, documentation, licensing, etc. A significant challenge is how to better make these tools cooperate and share components (provers, model checkers, syntax analysers, type checkers, transformation rules, etc.).