Prionsarebestknownastheagentsofmadcowandrelateddiseases,andagrowingnumberofproteinswithprion-likepropertieshavebeenimplicatedindiseasessuchasParkinson's.Butsomerecentlydiscoveredprion-likeproteinsdonotappeartoinducepathologicalchangesand,infact,maybekeyplayersinbasicbiologicalprocessessuchastranscription,immuneregulation,andmemoryformation.Writtenandeditedbyexpertsinthefield,thiscollectionfromColdSpringHarborPerspectivesinBiologyexaminestheexpandingrolesofprionsandprion-likeproteinsinhealthanddisease.Thecontributorsreviewthestructuresofprionsandprion-likeproteins,howtheyaggregateintoamyloidfibrilsandotherinsolublecomplexes,andtheuniquebiologicalpropertiesoftheaggregatedforms(e.g.,infectivity,gain/lossoffunction,andself-templating).Thenormalphysiologicalrolesofprion-likeproteins(e.g.,CPEBinthebrainandMAVSintheimmuneresponse)arediscussed,asistheformationofabnormalproteinaggregatesviaprion-likemechanismsinvarioushumandiseases.Theauthorsalsodiscussprionsinyeastandotherfungi,whichareconvenientmodelsforstudyingmechanismsofamyloidformationandpropagation.Thisvolumeisthereforeanessentialreferenceforbiochemists,cellandmolecularbiologists,andallwhowishtounderstandhowthesealternativelyfolded,self-propagatingproteinsfunction.