Startle and surprise are often cited as potentially contributing factors to aircraft incidents due to their possible negative effects on flightcrew performance. In this paper, we provide definitions of startle and surprise with the goal of delineating their differences. In the past, these terms have often been used interchangeably; however, there are distinctive conceptual, behavioral, and physiological differences between the startle reflex and the surprise emotion. Furthermore, we investigated the prevale nce of startle and surprise on the flight deck by examining voluntary incident reports in the Aviation Safety Reporting System (ASRS) and found surprise to be more prevalent than startle. Implications of these findings and limitations of our initial exploratory analysis are discussed.