After the 2011 Fukushima accidents, there is great uncertainty about the future of nuclear power. Many countries remain committed to the technology as a proven low-carbon source of baseload electricity; at the same time, few new construction projects have since been launched, in particular, because of uncertain economics, including enormous upfront capital costs of gigawatt-scale nuclear reactors. Partly in response to these developments, small modular reactors (SMRs) with power levels between 10 MWe and 300 MWe are now being considered as an alternative to established nuclear technologies. SMRs are designed to offer modularity so that upfront investments should be much smaller, while factory-based serial production could further help control overall costs of nuclear power. SMRs are also expected to have less stringent transport and siting requirements, thereby enabling installation in more diverse sites, including both off-grid in remote regions and, at the opposite end of the spectrum, perhaps also closer to urban areas. In this lecture, we will review these recent developments and discuss technical and policy challenges that SMRs would have to overcome before entering the market.