Back when we started writing the Message Passing library, we decided to put it into the "parallel" subdirectory (then the "mpi" sub-sub- directory), because we were hoping that "parallel" could become a top- level categorization for various parallel-programming libraries... threads, mpi, shared memory, etc. That may happen some day (when we manage to break Boost into pieces), but for now it's just a pain. Users need to using the longish namespace "boost::parallel::mpi", file names "boost/parallel/mpi", and run bjam with "bjam --with- parallel" (rather than "--with-mpi"). So, unless I hear screams, I'm going to move libs/parallel into libs/ mpi, boost/parallel into boost/mpi, and simplify its underlying directory structure a bit. When the time comes to split up Boost, and if it involves deeper namespaces, we'll make the change again then. For now, simpler is better. Cheers, Doug