The FCVODE interface module is a package of C functions which support the use of the CVODE solver, for the solution of ODE systems dy/dt = f (t, y), in a mixed FORTRAN/C setting. While CVODE is written in C, it is assumed here that the user’s calling program and user-supplied problem-defining routines are written in FORTRAN. This package provides the necessary interface to CVODE for both the serial and the parallel NVECTOR implementations.