In this chapter, we present an implementation of the Choice Reaction Time experiment. Choice reaction measures the time it takes to respond to the appearance of a stimulus with respect to which one must discriminate some specific property. Discovering the basic properties of how humans react to various presentation of stimuli (either single- or multi-modally) is an important aspect of human factors engineering research. Here you will have the opporotunity to test your reaction time when faced with stimuli whose properties you have to discern as quickly as possible.NOTE: For this unit, if you have not already done so (within the Basic Reaction Time experiment or the Stroop Effect experiment, for instance), you will need to download the IPL plugin. You will only need to do this once.