AbstractDeveloping systems that foster situation awareness in operators requires that stakeholders can make informed decisions about the design. These decisions must account for the operator’s underlying cognitive processes based on perception, comprehension, and projection of the system state. This chapter reviews the core cognitive processes responsible for monitoring and responding to changes in system state. Operators must perceive information before they can act in response, and the interface design affects operator accuracy and speed via known mechanisms (i.e., effects of color on visual search time). Perception of key information also relies on how the operator thinks during tasks, and certain design choices can support better attention control and detection of signals. After perceiving the information, operators also must comprehend and interpret the information. Design guidance and factors related to supporting comprehension are presented alongside explanations of how cognitive load and working memory affect the operator’s ability to develop and maintain a useful mental model of the system. This review of cognitive mechanisms gives designers a strong foundation to make informed decisions ranging from choosing an alarm color to assessing how much information should be on screen at once.