Increased flexibility at the grid edge is required to achieve ambitious climate goals and can be provided by smart energy solutions. By systematically reviewing the literature, we provide an overview of the potential flexibility of different residential electrical loads for France, Germany, Sweden, and the United Kingdom. While 85% of the studies aimed to identify potentials for shifting electrical energy use in time, the other 15% aimed to identify energy-saving potentials. Most of the data were found for the German and British electrical systems. A wide range of flexibility measures (e.g., price mechanisms, user-centered control strategies for space heating and water heating, automated shifting of appliances' use, EV charging algorithms, and consumer feedback) and methods (e.g., simulations, trials, and interviews) have been used. Potentials obtained from the literature have been upscaled to the national level, including corresponding effects in terms of carbon dioxide (CO2) emissions. The results show that between 2% and 18% of residential sector electricity in the four countries could be shifted, resulting in total emission reductions of 10 MtCO2 from peak shaving, or 24 MtCO2 per year if optimizing the deployment of renewables. The literature identifies substantial economic, technical, and behavioral benefits from implementing flexibility measures. In all the cases, it seems that the current regulatory framework would need to change to facilitate participation. Recognized risks include higher peaks and congestions in low price-hours and difficulties in designing electricity tariffs because of conflicts with CO2 intensity as well as potential instability in the entire electricity system caused by tariffs coupling to wholesale electricity pricing.