A key challenge for engineers and scientists over the coming decades is to develop and deploy power plants with sufficient capacity and flexibility to meet the growing demand for energy (mainly electrical) whilst simultaneously reducing emissions (primarily greenhouse gases). With fusion-based power plants not currently being considered viable for large-scale deployment for at least 40 years, other technologies must to be considered. Renewable and high efficiency combined gas-fired plants, along with nuclear solutions, are regarded as the most suitable candidates, with Small Modular Reactors (SMRs) developing as a favoured choice. However, two main impediments to the current deployment of SMRs exist: (1) safety concerns, particularly following the Fukushima accident, and (2) their economic models, with high capital costs only being available through a limited number of investors. The goal of this paper is to provide a review and a holistic assessment of this class of nuclear reactor, with specific focus on the most common technology: the Light Water Reactor (LWR). In particular, the paper provides a state-of-the-art assessment of their life cycle, along with a comparison of their relative merits with other base-load technologies. It is shown that SMRs are a suitable choice when the power to be installed is in the range 1-3 GWe and the social aspects of the investment, such as the creation of new employment positions, is a goal of policy makers. The paper thereby provides governments and stakeholders with key economic and social boundaries for the viable deployment of SMRs.