Radiofrequency　ablation　(RFA)　and　microwave　ablation　(MWA)　have　become　an　important　means　for　treating　liver　tumors.　RFA　and　MWA　are　a　minimally　invasive　therapy　which　involves　an　ablation　applicator　or　needle　(i.e.,　radiofrequency　electrode　or　microwave　antenna)　inserted　percutaneously　into　a　tumor　under　the　guidance　of　medical　imaging,　so　as　to　destroy　the　tumor　in　situ　by　heating-induced　coagulation　necrosis.　Treatment　planning,　particularly　needle　trajectory　planning,　is　crucial　to　RFA　and　MWA.　In　clinical　procedures,　however,　needle　trajectory　planning　still　relies　on　the　personal　experience　of　clinicians.　Manual　needle　trajectory　planning　is　tedious　and　may　cause　inter-operator　difference.　Therefore,　computer-assisted　needle　trajectory　planning　techniques　are　of　clinical　value　and　have　been　extensively　explored.　However,　a　literature　review　that　focuses　on　computer-assisted　needle　trajectory　planning　for　liver　tumor　RFA　and　MWA　has　not　been　reported.　In　this　paper,　we　conducted　an　extensive　review　on　computer-assisted　needle　trajectory　planning　for　RFA　and　MWA　of　liver　tumors.　Fundamentals　of　needle　trajectory　planning　are　summarized.　Algorithms　for　single-needle　and　multi-needle　trajectory　planning　are　analyzed.　Shortcomings　of　current　computer-assisted　needle　trajectory　planning　algorithms　are　discussed　and　future　developments　are　suggested.