Functional (ABC) assessment allows us to hypothesize the relations between environmental variables (antecedents and consequences) as well as the behavior being assessed. Functional analysis is the formal test of those hypotheses. Most often, assessing the ABCs of problem behaviors tells us what we need to know to replace the problem behavior and teach new skills. However, when a behavior is complex or high stakes, i.e., dangerous to the learner or the caregivers, functional analysis may be necessary. Conducting a functional analysis requires training and research skills, because the strategy is defined by arranging situations to produce the problem behavior. Functional analysis is the most precise, rigorous, and controlled method for demonstrating unambiguously the functional relationship between behavior and environment. That’s sexy!