MoI licenses are cross platform - you receive both the Windows and the Mac version installers and the same license key can be used with either or both of them.

The upgrade version requires a previous version license key in addition to the v4 license key that you will receive. You can order this version if you already own any previous version, including any of v3, v2, or v1 either EDU or commercial licenses. You can still order the upgrade even if you have skipped versions and do not have the latest.