A Practice Note reviewing the economic tools set out in the 2023 Merger Guidelines to assess whether and to what extent a merger between competitors is potentially anticompetitive. This Practice Note discusses the evidence that shows vulnerability to coordinated effects, such as the loss of a maverick, and the economic methods used to evaluate unilateral effects, including estimating a diversion ratio, conducting merger simulations, and using the Gross Upward Pricing Pressure Index test (GUPPI).