Cascade impaction is the primary method for determination of the aerodynamic particle size distribution (APSD) of orally inhaled drug products (OIDPs), due to some unique qualities. A cascade impactor fractionates the particles into discrete size bands based on particle inertia and therefore accounts for how those particles behave in a moving air stream. This makes the technique intuitively relevant to particle deposition in the lungs. Furthermore cascade impaction allows the determination of aerodynamic particle size specifically for the drug particles, by virtue of their collection and subsequent chemical analysis (typically by HPLC). "How Does a Cascade Impactor Work?" features that Andersen Cascade Impactor (ACI) which is a commonly used cascade impactor and features in both the United States Pharmacopeia (USP) and the European Pharmacopoeia (Ph. Eur.). We hope you enjoy it! Please note the animation is silent throughout.