This chapter introduces the key concepts and major theoretical accounts of cognitive control (e.g., conflict monitoring, the expected value of control) that seek to answer fundamental questions about the control mechanisms, the recruitment of control resources, the selection of task-relevant processes, and the prevention of interference. Although some of the theories focus more on the regulatory processes, while others on the evaluative mechanisms, most of them complement each other. Essential questions, such as the sources of capacity limitations, the continuum between control and automaticity, cognitive flexibility as a marker, the effects of contextual changes, and individual differences in both behavioral performance and neural activity are critically discussed throughout the chapter. The most widely used behavioral paradigms and their outcome measures (e.g., congruency effects, intrusion cost, switching cost, practice effects, post-error slowing and post-error reduction of interference) are presented and linked to different conceptual constructs.