Human factors have been well studied and widely disseminated in many high-stakes professions, especially aviation and the military. Until recently, however, medicine was a relative laggard even though our error rates have been just as concerning (Pruitt and Liebelt, Pediatr Emerg Care 26(12):942–948, 2010). Moreover, evidence has long argued that our traditional reliance on a fact-focused and classroom-based medical education is not “fit for task.” This is because it inadequately delivers the practical and non-technical skills required during medical crises, especially when there is stress, incomplete information, and complexity further increasing the likelihood of error and poor decision-making (Ripley, The unthinkable: who survives when disaster strikes. Three Rivers Press, 2008). The myriad of skills required of the modern trauma practitioner and trauma team mandates a more comprehensive, but also a more common sense, approach. This includes understanding the basics of psychology and human factor’s engineering. Specifically, this chapter covers the topic of situational awareness. We focus on trauma management, but these ideas apply throughout acute care medicine (Endsley, Hum Factors 37(1):32–64, 1995; Endsley, Situation awareness analysis and measurement. Lawrence Erlbaum Associates, 2000; St Pierre et al., Crisis management in acute care settings. Springer, 2011; Gaba et al., Hum Factors 37(1):20–31, 1995; Durso and Sethumadhavan, Hum Factors 50(3):442–448, 2008; Chabris and Simons, The invisible gorilla: and other ways our intuitions deceive us. Crown Publishers, Random House, 2010; Wickens, Hum Factors 50(3):397–403, 2008; Stanton et al., Saf Sci 39(39):189–204, 2001).