Hello, I have just started to learn myself parallel programming specifically MPI. I know that this is gonna be a silly question. I am trying to run the most basic 'hello world' program : program example1 implicit none !--Include the mpi header file include 'mpif.h' integer ierr,myid,numprocs integer irc !--Initialize MPI call MPI_INIT( ierr ) !--Who am I? --- get my rank=myid call MPI_COMM_RANK( MPI_COMM_WORLD, myid, ierr ) !--How many processes in the global group? call MPI_COMM_SIZE( MPI_COMM_WORLD, numprocs, ierr ) print *, "Process ",myid," of ",numprocs," is alive" !--Finalize MPI call MPI_FINALIZE(irc) stop end to compile ( test.f95 in my file's name ) f95 test.95 -o new But i get the Error: Can't open included file 'mpif.h' What is going on exactly?? is there something missing that i have to install?? Is there something wrong with the way i am trying to compile it ( if there was no error i should just type mpirun -np 3 new) Sorry for the silly question!!!