As　a　special　type　of　noncoding　RNA,　circular　RNAs　(circRNAs)　are　prevalent　in　many　organisms.　They　can　serve　as　sponges　for　microRNAs　and　protein　scaffolds,　or　templates　for　protein　translation,　making　them　linked　to　cellular　homeostasis　and　disease　progression.　In　recent　years,　circRNAs　have　been　found　to　be　abnormally　expressed　during　the　processes　of　viral　infection　and　pathogenesis,　and　can　help　a　virus　escape　the　immune　response　of　a　host.　Thus,　they　are　now　considered　to　play　important　functions　in　the　invasion　and　development　of　viruses.　Moreover,　the　potential　application　of　circRNAs　as　biomarkers　of　viral　infection　or　candidates　for　therapeutic　targeting　deserves　consideration.　This　review　summarizes　circRNAs　in　the　transcriptome,　including　their　classification,　production,　functions,　and　value　as　biomarkers.　This　review　paper　also　describes　research　progress　on　circRNAs　in　viral　infection　(mainly　hepatitis　B　virus,　HIV,　and　some　human　herpes　viruses)　and　aims　to　provide　new　ideas　for　antiviral　therapies　targeting　circRNAs.