The Flex Monitoring Team is conducting a multi-year evaluation of the Flex Program's Emergency Medical Services (EMS) Supplemental funding grant, awarded to eight grantees in 2019 to improve rural EMS in two focus areas: (1) development of sustainable models of care and (2) identification of rural-relevant EMS quality metrics and improvement of EMS data reporting. In this policy brief, the authors focus on the outcome measurement strategies of four of the grantees to support the development of a rural EMS evidence base. The brief examines grantees’ outcome measurement strategies including the outcome measures selected, the timing of those measures (e.g., short, intermediate, and long-term), the data sources used to support their outcome measures, and any challenges encountered by the grantees in monitoring project outcomes. We also provide recommendations to refine the grantees’ outcome measurement strategies.