Situational judgment tests (SJTs) are personnel selection instruments that present job applicants with work-related situations and possible responses to the situations. There are typically 2 types of instructions: behavioral tendency and knowledge. Behavioral tendency instructions ask respondents to identify how they would likely behave in a given situation. Knowledge instructions ask respondents to evaluate the effectiveness of possible responses to a given situation. Results showed that response instructions influenced the constructs measured by the tests. Tests with knowledge instructions had higher correlations with cognitive ability. Tests with behavioral tendency instructions showed higher correlations with personality constructs. Results also showed that response instructions had little moderating effect on criterion-related validity. Supplemental analyses showed that the moderating effect of response instructions on construct validity was not due to systematic differences in item content. SJTs have incremental validity over cognitive ability, the Big 5, and over a composite of cognitive ability and the Big 5.