Electrostatic precipitator is the most efficient device used for the removal of fly ash particles from the flue gases produced by coal-fired boilers in power plants. However, the fractional collection efficiency of electrostatic precipitators steeply decreases for particles smaller than 1 mu m, and particles in the size range of 200-500 nm are removed with lower collection efficiency than those outside this range. These particles are dangerous to humans and have detrimental environmental effects, so there is a need for novel more efficient technologies for their control. One of the answers to this challenge is the two-stage electrostatic precipitator, in which the electrostatic charging and precipitation processes have been separated. The PM2.5 particles (of a size < 2.5 mu m) are electrically charged in a separate device (precharger) to a maximal possible electric charge, and then precipitated in a parallel plate collector, free of corona discharge. The electric field in the collection stage can be higher than in an electrostatic precipitator due to the lack of sharp discharge points. A higher electric field allows an increase of the collection efficiency for PM2.5 particles. Another solution is the agglomeration of submicron particles to form larger particles before their precipitation by a parallel-plate collector, conventional electrostatic precipitator or any other gas cleaning device. In some of the reviewed devices, both of these processes were combined in a single device that allowed further increases in the collection efficiency for submicron particles. Devices of this type have been tested in a labor semi-industrial scale for the removal of PM2.5 particles from flue gases or diesel engine exhausts. In this paper, various constructions of two-stage electrostatic precipitators, comprising a precharger and/or agglomerator in the first stage, and an electrostatic collector in the second stage, have been reviewed. Some of these devices were able to increase the mass collection efficiency above 95% for PM2.5 particles. (C) 2018 Elsevier Ltd. All rights reserved.