The primary objectives of this study are to: • Confirm the efficacy of aliskiren 75 mg, 150 mg and 300 mg in patients with essential hypertension by testing the hypothesis of superior reduction in MSDBP from baseline to study end when compared to placebo. • Demonstrate the efficacy of the combination of aliskiren and HCTZ 75/6.25 mg, 75/12.5 mg, 150/6.25 mg, 150/12.5 mg, 150/25 mg, 300/12.5 mg and 300/25 mg in patients with essential hypertension by testing the hypothesis of superior reduction in MSDBP from baseline to study end when compared to the component monotherapies.