In some experiments, the acquired data need to be processed in real time and appropriate action has to be taken based on the processed result. Such a comprehensive and stringent requirement demands a data acquisition system possessing the necessary characteristics of speed, power, and so on. Presently there are several systems commercially available for rapidly collecting a large amount of data, processing it, and displaying the desired results in visual and printed forms. But such commercially available units are expensive and most of them are not flexible in their configurations. For laboratory research experiments with a limited number of transducers, low-cost data acquisition units can be configured. Such systems have become popular alternatives to a standalone system. These PC-based or microprocessor-based laboratory systems are highly flexible in their configurations and therefore, a host of options and expansion possibilities are available with them. This chapter discusses data acquisition systems, and the functions of the elements that go together to make up an overall data acquisition and processing installation, with attention focused mainly on the general principles and their applications to PC-based systems.