This chapter focuses on the design fundamentals of low-voltage charge pumps. The circuit structure and operation are overviewed. The circuit is composed of switches and capacitors. There are a variety of switches with different combinations of transistors. Several types of capacitors have also been fabricated in integrated circuits. The parasitic capacitance of the switches and the capacitors affects the characteristics of the charge pump. The circuit area is considered the cost. The area of the charge pump is mainly determined by the capacitor because a switch is nominally much smaller than a capacitor. The output current–voltage equation of a charge pump operating at low voltage is found as a function of the design and device parameters. One can estimate an output current at a specific output voltage once all the design and device parameters are given. Conversely, to design charge pumps operating at low voltage, a required output current at a specific output voltage is given, and then all the design parameters need to be determined in a specific CMOS technology where all the device parameters are given. The method for designing the charge pump to meet the required specification with a minimum circuit area is described. There is a trade-off between the circuit area and power conversion efficiency. As the power supply voltage decreases, the circuit area and the power efficiency tend to increase exponentially and decrease gradually, respectively. When the power supply voltage is one of the design parameters, one must determine the operating voltage, the circuit area and the power efficiency according to one’s priority.