A supervisory control and data acquisition (SCADA) is a system which collects field data from dispersed field locations, transfers it to a central computer facility, and displays the information so gathered on the operator's panel. This chapter describes the first-generation, second-generation, third generation, and fourth-generation SCADA systems. It includes a table that shows the differences between the different generations of SCADA systems. In a SCADA, enormous amount of data are generated from numerous sensors, actuators, and others situated at geographically separated locations. These data at multiple locations need to be transported at a central location for storing, analysis, display, and subsequent control actions to be taken by the master control unit. SCADA software are divided into two types: open and proprietary. Open system software are far more popular because of the interoperability that they bring to the system. Proprietary software are closed ended because they can be used only with the hardware supplied by the same manufacturer.