Hypertension is a highly prevalent condition and, as a risk factor for vascular disease in particular, a leading contributory cause of death worldwide. Recent consensus guidelines suggest that moderate and severe (grade II and III) hypertension should be treated rapidly to achieve targets though, prior to the inception of this thesis, the evidence for the safety and efficacy of this approach, together with the physiological consequences of rapid hypertension treatment in moderate and severe disease, was limited. This thesis explores the clinical consequences of an 18-week treatment programme for individuals with grade II and III hypertension, using guideline- recommended pharmacological treatment, delivered over an accelerated timeframe. The blood pressure response to treatment is reported, together with the tolerance and safety of the protocol, as defined by the protocol completion rate, frequency of medication side effects and clinically significant adverse events. The programme also provided an opportunity to study health-rated quality of life in patients with moderate and severe hypertension and the effect of rapid treatment on health-related quality of life. This allowed for the first validation (according to modern standards) of an English language disease-specific instrument for measuring health-related quality of life in hypertension, following translation of the original MINICHAL disease-specific instrument from the original Spanish. In addition, the clinical treatment programme provided an opportunity to study the microvascular response to rapid treatment of moderate and severe hypertension, particularly with relevance to the rarefaction of hypertension and its reversal with treatment. Moreover, the morphological and functional myocardial consequences of treatment were determined, using cardiac MR imaging. Accordingly, this thesis presents evidence supporting the rapid treatment of moderate and severe hypertension, providing an opportunity for this to be studied in future investigations, with the aim of exploring whether this approach is prognostically advantageous for patients.