Each quality improvement (QI) project has an implicit study design, although these designs are not discussed as commonly as they are in clinical research. Most QI projects fall under the quasi-experimental study category, in which observations are made before and after the implementation of an intervention(s). The simplest and most commonly used for QI studies is the pre-post design, in which observations are made before and after each intervention that was implemented over a specified period. More sophisticated designs for QI studies enable a study team to draw stronger inferences about the system that is being changed and the individual effects of the interventions that are implemented. In the final commentary in this QI series, we discuss these study designs and focus on the strengths and weaknesses of more sophisticated designs, including cluster randomized, stepped-wedge, and factorial designs.