The Russia-Ukraine war (2022-) has highlighted the ways in which civilians can support a nation's effort to defend itself against an external occupying power. Although civilian-based resistance began during the first hours of Russia's full-scale invasion of Ukraine in 2022, most analysis to date has focused on Russian-Ukrainian armed military confrontations. Ukrainian civilian resistance efforts merit attention because of their potential value in helping Ukraine's strategic aims to ensure victory by regaining territorial integrity and maintaining political sovereignty. The authors of this report offer a broad characterization of Ukrainian approaches to civilian-based resistance during the first four months of the conflict. First, the authors offer a short overview of pertinent historic examples of civilian-based resistance and opposition movements that have paved the way for stronger social mobilization and activism across all segments of Ukrainian society. Second, the authors offer an overview of Ukrainian civilian-based activities through an analytical framework developed by RAND Corporation researchers in 2021 to analyze civilian-based resistance against external occupation. Third, the authors identify indicative future trends in civilian-based resistance against external aggressors.