Building scenarios for training recognition skills in complex domains requires the addition of hard-to-detect cues and unexpected events. This chapter describes the Periphery Principle, which emphasizes the importance of including critical cues in nonobvious ways so trainees learn how to seek them, and the Perturbation Principle, which encourages training designers to incorporate unexpected events into training scenarios so trainees learn to adapt to novel situations. The chapter presents methods for identifying peripheral cues and important perturbations for a particular domain or task, and gives examples of critical cue inventories and complexity tables that can be useful tools for training designers.