Christophe, One problem I've run into with the EUML frontend is the the _EVENT, _ACTION and _STATE macros define non-static instance variables. So, if I define a state machine in a header file which then gets included in multiple source files (e.g. I have two classes which use the same state machine) I get linker errors about duplicate instances. For states, I can work around this issue by doing, for example, BOOST_MSM_EUML_DECLARE_STATE((),MyStateType) static MyStateType MyState; and then using MyState in the transition table. Events and Actions don't seem to have the corresponding _DECLARE_ macros, so this workaround isn't really feasible at this point in time. Any thoughts? Thanks Nate