Instructional technology research is broad both in terms of topics and explorations of basic and applied research. In this chapter, we examine various types of stimulus materials that instructional technology researchers have used to study different phenomena. Specifically, we discuss and illustrate how the choice of stimulus material (e.g., actual lesson content, pictures, prose, etc.) directly influences the internal validity (rigor) and external validity (generalizability) of the findings. While randomized experiments are considered the so-called gold standard (Slavin, Educational Researcher 37(1):5–14, 2008) of educational research, particularly for evaluating the effectiveness of instructional strategies, these studies may employ artificial or novel stimulus materials that can limit generalization of the results. Since one goal of instructional technology research is to provide evidence that allows the instructional designer to generate heuristics easily applicable (i.e., generalized) to new situations, studies with strong external validity should be highly desired. Similarly, there are also instances where initial studies need to be designed with high internal validity, sometimes at the sacrifice of external validity, to control for extraneous variables. Using selected studies as illustrative examples, this chapter examines how validity has been addressed in instructional technology research.