An　unprecedented　infodemic　has　been　witnessed　to　create　massive　damage　to　human　society.　However,　it　was　not　thoroughly　investigated.　This　systematic　review　aims　to　(1)　synthesize　the　existing　literature　on　the　causes　and　impacts　of　COVID-19　infodemic;　(2)　summarize　the　proposed　strategies　to　fight　with　COVID-19　infodemic;　and　(3)　identify　the　directions　for　future　research.　A　systematic　literature　search　following　the　PRISMA　guideline　covering　12　scholarly　databases　was　conducted　to　retrieve　various　types　of　peer-reviewed　articles　that　reported　causes,　impacts,　or　countermeasures　of　the　infodemic.　Empirical　studies　were　assessed　for　risk　of　bias　using　the　Mixed-Methods　Appraisal　Tool.　A　coding　theme　was　iteratively　developed　to　categorize　the　causes,　impacts,　and　countermeasures　found　from　the　included　studies.　Social　media　usage,　low　level　of　health/eHealth　literacy,　and　fast　publication　process　and　preprint　service　are　identified　as　the　major　causes　of　the　infodemic.　Besides,　the　vicious　circle　of　human　rumor-spreading　behavior　and　the　psychological　issues　from　the　public　(e.g.,　anxiety,　distress,　fear)　emerges　as　the　characteristic　of　the　infodemic.　Comprehensive　lists　of　countermeasures　are　summarized　from　different　perspectives,　among　which　risk　communication　and　consumer　health　information　need/seeking　are　of　particular　importance.　Theoretical　and　practical　implications　are　discussed　and　future　research　directions　are　suggested.　©　2021