This was a randomized, double-blind study comparing the efficacy and safety of ruxolitinib (INCB018424) tablets to matching placebo tablets in patients diagnosed with Myelofibrosis (either Primary Myelofibrosis (PMF) or Post-Polycythemia Vera Myelofibrosis (PPV-MF) or Post-Essential Thrombocythemia Myelofibrosis (PET-MF).