Micromagnetic simulations are specified to the OOMMF solvers using the OOMMF Micromagnetic Input Format (MIF). There are four distinct versions of this format. The oldest format, version 1.1, is used by the mmSolve 2D solvers (mmSolve2D and batchsolve) and the mmProbEd problem editor. The MIF 2.1 and MIF 2.2 formats are the powerful, native format used by the Oxs 3D solvers. The MIF 1.2 format is a minor modification to the 1.1 format, which can be used as a simple but restricted interface to the Oxs solvers. In all cases values are specified in SI units. A command line utility mifconvert is provided to aid in converting MIF 1.1 files to the MIF 2.1 format. For all versions it is recommended that MIF files be given names ending with the .mif file extension.