This chapter starts by reviewing the main concepts of the analog-to-digital converter (ADC) and the data acquisition system. Issues of sampling, quantization error, and aliasing are considered. The mbed ADC capability is introduced, first through simple applications, such as reading the value of a potentiometer. ADC digital output values are then processed and displayed on the host computer screen, requiring the mbed to be configured to make this data transfer. Inputs from simple sensors, a light-dependent resistor and integrated circuit temperature sensor, are converted, scaled, and displayed to computer screen. Conversion time is measured and evaluated, and Nyquist's sampling theorem is explored.