Long　before　the　proposal　of　the　concept　of　high-entropy　alloy,　researchers　have　observed　the　strong　dependence　of　ion　irradiation　induced　swelling　on　the　concentration　of　principal　elements　in　the　Fe-Cr-Ni　alloy　system　in　1970s.　Nonetheless,　the　underlying　physics　of　such　dependence　was　not　systematically　investigated,　and　principal　elements　were　rarely　targeted　in　design　of　irradiation　resistant　alloys,　until　the　recent　development　of　high-entropy　alloys.　This　new　family　of　alloys　greatly　expands　the　compositional　space　for　alloy　design,　and　provides　an　ideal　playground　of　studying　the　impact　of　principal　alloy　elements　on　the　irradiation　response.　In　the　recent　years,　significant　experimental　effort　has　been　made　to　understand　the　impact　of　number,　type,　and　concentration　of　alloying　elements　on　the　irradiation　(by　ions,　electrons,　and　neutrons)　induced　microstructural　evolution　and　property　degradation.　The　up-to-date　results　have　revealed　that,　defect　evolution　process　is　retarded　in　the　alloys　with　high　chemical　complexity,　through　tuning　the　energy　dissipation　and　the　defect　formation　and　migration　energies.　For　example,　the　size　of　interstitial　clusters　is　reduced,　and　the　formation　and　growth　of　voids　and　helium　bubbles　are　suppressed.　It　has　been　evidenced　that　proper　modification　of　principal　elements　can　indeed　improve　the　irradiation　resistance　of　alloys,　however,　considerable　discrepancies　have　also　been　observed　regarding　the　irradiation-induced　phase　instability,　swelling,　and　hardening　for　different　alloy　systems　and　irradiation　conditions.　Therefore,　a　conclusive　evaluation　cannot　be　made　on　whether　the　irradiation　resistance　of　high-entropy　alloys　is　overall　superior.　We　review　the　major　progress　in　experimental　studies　on　irradiation　effects　of　high-entropy　alloys,　and　summarize　the　current　understanding　and　evaluation　of　the　irradiation　resistance.　The　limitations　or　contradictions　of　experimental　results　are　discussed,　and　perspectives　are　provided　for　the　future　studies　in　this　field.　©　2020,　Materials　Review　Magazine.　All　right　reserved.