The ancillary services are important for maintaining the grid stability and power quality in modern power systems. High penetration of renewable energy sources and increase in the loading levels lead to voltage rise and voltage drop in the distribution network, respectively. Therefore voltage control is an important ancillary service in distribution systems. In this chapter the use of smart transformer for voltage control in low-voltage (LV) distribution systems is discussed. There are two types of voltage-control methods, that is, set points–based voltage-control method and full output voltage range–based method. In set points–based control the output voltage is chosen from the predefined set points. In a full output voltage range–based control, the output voltage is infinitely adjustable within its range. The application of both these voltage-control methods for improving the voltage profile in LV distribution network is presented through different case studies.