Scrum Guide 2020 - CertiProf

The Scrum Guide documents Scrum as developed, evolved, and sustained for 30-plus years by Jeff Sutherland and Ken Schwaber. Other sources provide patterns, ... 636338220064551 USD SkiptoMainContent ScrumGuide2020 The2020ScrumGuideTM   PurposeoftheScrumGuide WedevelopedScrumintheearly1990s.WewrotethefirstversionoftheScrumGuidein2010tohelppeopleworldwideunderstandScrum.WehaveevolvedtheGuidesincethenthroughsmall,functionalupdates.Together,westandbehindit. TheScrumGuidecontainsthedefinitionofScrum.EachelementoftheframeworkservesaspecificpurposethatisessentialtotheoverallvalueandresultsrealizedwithScrum.ChangingthecoredesignorideasofScrum,leavingoutelements,ornotfollowingtherulesofScrum,coversupproblemsandlimitsthebenefitsofScrum,potentiallyevenrenderingituseless. WefollowthegrowinguseofScrumwithinanever-growingcomplexworld.WearehumbledtoseeScrumbeingadoptedinmanydomainsholdingessentiallycomplexwork,beyondsoftwareproductdevelopmentwhereScrumhasitsroots.AsScrum’susespreads,developers,researchers,analysts,scientists,andotherspecialistsdothework.Weusetheword“developers”inScrumnottoexclude,buttosimplify.IfyougetvaluefromScrum,consideryourselfincluded. AsScrumisbeingused,patterns,processes,andinsightsthatfittheScrumframeworkasdescribedinthisdocument,maybefound,appliedanddevised.TheirdescriptionisbeyondthepurposeoftheScrumGuidebecausetheyarecontextsensitiveanddifferwidelybetweenScrumuses.SuchtacticsforusingwithintheScrumframeworkvarywidelyandaredescribedelsewhere. ScrumDefinition Scrumisalightweightframeworkthathelpspeople,teamsandorganizationsgeneratevaluethroughadaptivesolutionsforcomplexproblems. Inanutshell,ScrumrequiresaScrumMastertofosteranenvironmentwhere: AProductOwnerorderstheworkforacomplexproblemintoaProductBacklog. TheScrumTeamturnsaselectionoftheworkintoanIncrementofvalueduringaSprint. TheScrumTeamanditsstakeholdersinspecttheresultsandadjustforthenextSprint. Repeat Scrumissimple.Tryitasisanddetermineifitsphilosophy,theory,andstructurehelptoachievegoalsandcreatevalue.TheScrumframeworkispurposefullyincomplete,onlydefiningthepartsrequiredtoimplementScrumtheory.Scrumisbuiltuponbythecollectiveintelligenceofthepeopleusingit.Ratherthanprovidepeoplewithdetailedinstructions,therulesofScrumguidetheirrelationshipsandinteractions. Variousprocesses,techniquesandmethodscanbeemployedwithintheframework.Scrumwrapsaroundexistingpracticesorrendersthemunnecessary.Scrummakesvisibletherelativeefficacyofcurrentmanagement,environment,andworktechniques,sothatimprovementscanbemade. ScrumTheory Scrumisfoundedonempiricismandleanthinking.Empiricismassertsthatknowledgecomesfromexperienceandmakingdecisionsbasedonwhatisobserved.Leanthinkingreduceswasteandfocusesontheessentials. Scrumemploysaniterative,incrementalapproachtooptimizepredictabilityandtocontrolrisk.Scrumengagesgroupsofpeoplewhocollectivelyhavealltheskillsandexpertisetodotheworkandshareoracquiresuchskillsasneeded. Scrumcombinesfourformaleventsforinspectionandadaptationwithinacontainingevent,theSprint.TheseeventsworkbecausetheyimplementtheempiricalScrumpillarsoftransparency,inspection,andadaptation. Transparency Theemergentprocessandworkmustbevisibletothoseperformingtheworkaswellasthosereceivingthework.WithScrum,importantdecisionsarebasedontheperceivedstateofitsthreeformalartifacts.Artifactsthathavelowtransparencycanleadtodecisionsthatdiminishvalueandincreaserisk. Transparencyenablesinspection.Inspectionwithouttransparencyismisleadingandwasteful. Inspection TheScrumartifactsandtheprogresstowardagreedgoalsmustbeinspectedfrequentlyanddiligentlytodetectpotentiallyundesirablevariancesorproblems.Tohelpwithinspection,Scrumprovidescadenceintheformofitsfiveevents. Inspectionenablesadaptation.Inspectionwithoutadaptationisconsideredpointless.Scrumeventsaredesignedtoprovokechange. Adaptation Ifanyaspectsofaprocessdeviateoutsideacceptablelimitsoriftheresultingproductisunacceptable,theprocessbeingappliedorthematerialsbeingproducedmustbeadjusted.Theadjustmentmustbemadeassoonaspossibletominimizefurtherdeviation. Adaptationbecomesmoredifficultwhenthepeopleinvolvedarenotempoweredorself-managing.AScrumTeamisexpectedtoadaptthemomentitlearnsanythingnewthroughinspection. ScrumValues SuccessfuluseofScrumdependsonpeoplebecomingmoreproficientinlivingfivevalues: Commitment,Focus,Openness,Respect,andCourage TheScrumTeamcommitstoachievingitsgoalsandtosupportingeachother.TheirprimaryfocusisontheworkoftheSprinttomakethebestpossibleprogresstowardthesegoals.TheScrumTeamanditsstakeholdersareopenabouttheworkandthechallenges.ScrumTeammembersrespecteachothertobecapable,independentpeople,andarerespectedassuchbythepeoplewithwhomtheywork.TheScrumTeammembershavethecouragetodotherightthing,toworkontoughproblems. ThesevaluesgivedirectiontotheScrumTeamwithregardtotheirwork,actions,andbehavior.Thedecisionsthataremade,thestepstaken,andthewayScrumisusedshouldreinforcethesevalues,notdiminishorunderminethem.TheScrumTeammemberslearnandexplorethevaluesastheyworkwiththeScrumeventsandartifacts.WhenthesevaluesareembodiedbytheScrumTeamandthepeopletheyworkwith,theempiricalScrumpillarsoftransparency,inspection,andadaptationcometolifebuildingtrust. ScrumTeam ThefundamentalunitofScrumisasmallteamofpeople,aScrumTeam.TheScrumTeamconsistsofoneScrumMaster,oneProductOwner,andDevelopers.WithinaScrumTeam,therearenosub-teamsorhierarchies.Itisacohesiveunitofprofessionalsfocusedononeobjectiveatatime,theProductGoal. ScrumTeamsarecross-functional,meaningthemembershavealltheskillsnecessarytocreatevalueeachSprint.Theyarealsoself-managing,meaningtheyinternallydecidewhodoeswhat,when,andhow. TheScrumTeamissmallenoughtoremainnimbleandlargeenoughtocompletesignificantworkwithinaSprint,typically10orfewerpeople.Ingeneral,wehavefoundthatsmallerteamscommunicatebetterandaremoreproductive.IfScrumTeamsbecometoolarge,theyshouldconsiderreorganizingintomultiplecohesiveScrumTeams,eachfocusedonthesameproduct.Therefore,theyshouldsharethesameProductGoal,ProductBacklog,andProductOwner. TheScrumTeamisresponsibleforallproduct-relatedactivitiesfromstakeholdercollaboration,verification,maintenance,operation,experimentation,researchanddevelopment,andanythingelsethatmightberequired.Theyarestructuredandempoweredbytheorganizationtomanagetheirownwork.WorkinginSprintsatasustainablepaceimprovestheScrumTeam’sfocusandconsistency. TheentireScrumTeamisaccountableforcreatingavaluable,usefulIncrementeverySprint.ScrumdefinesthreespecificaccountabilitieswithintheScrumTeam:theDevelopers,theProductOwner,andtheScrumMaster. Developers DevelopersarethepeopleintheScrumTeamthatarecommittedtocreatinganyaspectofausableIncrementeachSprint. ThespecificskillsneededbytheDevelopersareoftenbroadandwillvarywiththedomainofwork.However,theDevelopersarealwaysaccountablefor: CreatingaplanfortheSprint,theSprintBacklog; InstillingqualitybyadheringtoaDefinitionofDone; AdaptingtheirplaneachdaytowardtheSprintGoal;and, Holdingeachotheraccountableasprofessionals. ProductOwner TheProductOwnerisaccountableformaximizingthevalueoftheproductresultingfromtheworkoftheScrumTeam.Howthisisdonemayvarywidelyacrossorganizations,ScrumTeams,andindividuals. TheProductOwnerisalsoaccountableforeffectiveProductBacklogmanagement,whichincludes: DevelopingandexplicitlycommunicatingtheProductGoal; CreatingandclearlycommunicatingProductBacklogitems; OrderingProductBacklogitems;and, EnsuringthattheProductBacklogistransparent,visibleandunderstood. TheProductOwnermaydotheaboveworkormaydelegatetheresponsibilitytoothers.Regardless,theProductOwnerremainsaccountable. ForProductOwnerstosucceed,theentireorganizationmustrespecttheirdecisions.ThesedecisionsarevisibleinthecontentandorderingoftheProductBacklog,andthroughtheinspectableIncrementattheSprintReview. TheProductOwnerisoneperson,notacommittee.TheProductOwnermayrepresenttheneedsofmanystakeholdersintheProductBacklog.ThosewantingtochangetheProductBacklogcandosobytryingtoconvincetheProductOwner. ScrumMaster TheScrumMasterisaccountableforestablishingScrumasdefinedintheScrumGuide.TheydothisbyhelpingeveryoneunderstandScrumtheoryandpractice,bothwithintheScrumTeamandtheorganization. TheScrumMasterisaccountablefortheScrumTeam’seffectiveness.TheydothisbyenablingtheScrumTeamtoimproveitspractices,withintheScrumframework. ScrumMastersaretrueleaderswhoservetheScrumTeamandthelargerorganization. TheScrumMasterservestheScrumTeaminseveralways,including: Coachingtheteammembersinself-managementandcross-functionality; HelpingtheScrumTeamfocusoncreatinghigh-valueIncrementsthatmeettheDefinitionofDone; CausingtheremovalofimpedimentstotheScrumTeam’sprogress;and, EnsuringthatallScrumeventstakeplaceandarepositive,productive,andkeptwithinthetimebox. TheScrumMasterservestheProductOwnerinseveralways,including: HelpingfindtechniquesforeffectiveProductGoaldefinitionandProductBacklogmanagement; HelpingtheScrumTeamunderstandtheneedforclearandconciseProductBacklogitems; Helpingestablishempiricalproductplanningforacomplexenvironment;and, Facilitatingstakeholdercollaborationasrequestedorneeded. TheScrumMasterservestheorganizationinseveralways,including: Leading,training,andcoachingtheorganizationinitsScrumadoption; PlanningandadvisingScrumimplementationswithintheorganization; Helpingemployeesandstakeholdersunderstandandenactanempiricalapproachforcomplexwork;and, RemovingbarriersbetweenstakeholdersandScrumTeams. ScrumEvents TheSprintisacontainerforallotherevents.EacheventinScrumisaformalopportunitytoinspectandadaptScrumartifacts.Theseeventsarespecificallydesignedtoenablethetransparencyrequired.Failuretooperateanyeventsasprescribedresultsinlostopportunitiestoinspectandadapt.EventsareusedinScrumtocreateregularityandtominimizetheneedformeetingsnotdefinedinScrum. Optimally,alleventsareheldatthesametimeandplacetoreducecomplexity. TheSprint SprintsaretheheartbeatofScrum,whereideasareturnedintovalue. Theyarefixedlengtheventsofonemonthorlesstocreateconsistency.AnewSprintstartsimmediatelyaftertheconclusionofthepreviousSprint. AlltheworknecessarytoachievetheProductGoal,includingSprintPlanning,DailyScrums,SprintReview,andSprintRetrospective,happenwithinSprints. DuringtheSprint: NochangesaremadethatwouldendangertheSprintGoal; Qualitydoesnotdecrease; TheProductBacklogisrefinedasneeded;and, ScopemaybeclarifiedandrenegotiatedwiththeProductOwnerasmoreislearned. SprintsenablepredictabilitybyensuringinspectionandadaptationofprogresstowardaProductGoalatleasteverycalendarmonth.WhenaSprint’shorizonistoolongtheSprintGoalmaybecomeinvalid,complexitymayrise,andriskmayincrease.ShorterSprintscanbeemployedtogeneratemorelearningcyclesandlimitriskofcostandefforttoasmallertimeframe.EachSprintmaybeconsideredashortproject. Variouspracticesexisttoforecastprogress,likeburn-downs,burn-ups,orcumulativeflows.Whileprovenuseful,thesedonotreplacetheimportanceofempiricism.Incomplexenvironments,whatwillhappenisunknown.Onlywhathasalreadyhappenedmaybeusedforforward-lookingdecisionmaking. ASprintcouldbecancellediftheSprintGoalbecomesobsolete.OnlytheProductOwnerhastheauthoritytocanceltheSprint. SprintPlanning SprintPlanninginitiatestheSprintbylayingouttheworktobeperformedfortheSprint.ThisresultingplaniscreatedbythecollaborativeworkoftheentireScrumTeam. TheProductOwnerensuresthatattendeesarepreparedtodiscussthemostimportantProductBacklogitemsandhowtheymaptotheProductGoal.TheScrumTeammayalsoinviteotherpeopletoattendSprintPlanningtoprovideadvice. SprintPlanningaddressesthefollowingtopics: TopicOne:WhyisthisSprintvaluable? TheProductOwnerproposeshowtheproductcouldincreaseitsvalueandutilityinthecurrentSprint.ThewholeScrumTeamthencollaboratestodefineaSprintGoalthatcommunicateswhytheSprintisvaluabletostakeholders.TheSprintGoalmustbefinalizedpriortotheendofSprintPlanning. TopicTwo:WhatcanbeDonethisSprint? ThroughdiscussionwiththeProductOwner,theDevelopersselectitemsfromtheProductBacklogtoincludeinthecurrentSprint.TheScrumTeammayrefinetheseitemsduringthisprocess,whichincreasesunderstandingandconfidence. SelectinghowmuchcanbecompletedwithinaSprintmaybechallenging.However,themoretheDevelopersknowabouttheirpastperformance,theirupcomingcapacity,andtheirDefinitionofDone,themoreconfidenttheywillbeintheirSprintforecasts. TopicThree:Howwillthechosenworkgetdone? ForeachselectedProductBacklogitem,theDevelopersplantheworknecessarytocreateanIncrementthatmeetstheDefinitionofDone.ThisisoftendonebydecomposingProductBacklogitemsintosmallerworkitemsofonedayorless.HowthisisdoneisatthesolediscretionoftheDevelopers.NooneelsetellsthemhowtoturnProductBacklogitemsintoIncrementsofvalue. TheSprintGoal,theProductBacklogitemsselectedfortheSprint,plustheplanfordeliveringthemaretogetherreferredtoastheSprintBacklog. SprintPlanningistimeboxedtoamaximumofeighthoursforaone-monthSprint.ForshorterSprints,theeventisusuallyshorter. DailyScrum ThepurposeoftheDailyScrumistoinspectprogresstowardtheSprintGoalandadapttheSprintBacklogasnecessary,adjustingtheupcomingplannedwork. TheDailyScrumisa15-minuteeventfortheDevelopersoftheScrumTeam.Toreducecomplexity,itisheldatthesametimeandplaceeveryworkingdayoftheSprint.IftheProductOwnerorScrumMasterareactivelyworkingonitemsintheSprintBacklog,theyparticipateasDevelopers. TheDeveloperscanselectwhateverstructureandtechniquestheywant,aslongastheirDailyScrumfocusesonprogresstowardtheSprintGoalandproducesanactionableplanforthenextdayofwork.Thiscreatesfocusandimprovesself-management. DailyScrumsimprovecommunications,identifyimpediments,promotequickdecision-making,andconsequentlyeliminatetheneedforothermeetings. TheDailyScrumisnottheonlytimeDevelopersareallowedtoadjusttheirplan.Theyoftenmeetthroughoutthedayformoredetaileddiscussionsaboutadaptingorre-planningtherestoftheSprint’swork. SprintReview ThepurposeoftheSprintReviewistoinspecttheoutcomeoftheSprintanddeterminefutureadaptations.TheScrumTeampresentstheresultsoftheirworktokeystakeholdersandprogresstowardtheProductGoalisdiscussed. Duringtheevent,theScrumTeamandstakeholdersreviewwhatwasaccomplishedintheSprintandwhathaschangedintheirenvironment.Basedonthisinformation,attendeescollaborateonwhattodonext.TheProductBacklogmayalsobeadjustedtomeetnewopportunities.TheSprintReviewisaworkingsessionandtheScrumTeamshouldavoidlimitingittoapresentation. TheSprintReviewisthesecondtolasteventoftheSprintandistimeboxedtoamaximumoffourhoursforaone-monthSprint.ForshorterSprints,theeventisusuallyshorter. SprintRetrospective ThepurposeoftheSprintRetrospectiveistoplanwaystoincreasequalityandeffectiveness. TheScrumTeaminspectshowthelastSprintwentwithregardstoindividuals,interactions,processes,tools,andtheirDefinitionofDone.Inspectedelementsoftenvarywiththedomainofwork.Assumptionsthatledthemastrayareidentifiedandtheiroriginsexplored.TheScrumTeamdiscusseswhatwentwellduringtheSprint,whatproblemsitencountered,andhowthoseproblemswere(orwerenot)solved. TheScrumTeamidentifiesthemosthelpfulchangestoimproveitseffectiveness.Themostimpactfulimprovementsareaddressedassoonaspossible.TheymayevenbeaddedtotheSprintBacklogforthenextSprint. TheSprintRetrospectiveconcludestheSprint.Itistimeboxedtoamaximumofthreehoursforaone-monthSprint.ForshorterSprints,theeventisusuallyshorter. ScrumArtifacts Scrum’sartifactsrepresentworkorvalue.Theyaredesignedtomaximizetransparencyofkeyinformation.Thus,everyoneinspectingthemhasthesamebasisforadaptation. Eachartifactcontainsacommitmenttoensureitprovidesinformationthatenhancestransparencyandfocusagainstwhichprogresscanbemeasured: FortheProductBacklogitistheProductGoal. FortheSprintBacklogitistheSprintGoal. FortheIncrementitistheDefinitionofDone. ThesecommitmentsexisttoreinforceempiricismandtheScrumvaluesfortheScrumTeamandtheirstakeholders. ProductBacklog TheProductBacklogisanemergent,orderedlistofwhatisneededtoimprovetheproduct.ItisthesinglesourceofworkundertakenbytheScrumTeam. ProductBacklogitemsthatcanbeDonebytheScrumTeamwithinoneSprintaredeemedreadyforselectioninaSprintPlanningevent.Theyusuallyacquirethisdegreeoftransparencyafterrefiningactivities.ProductBacklogrefinementistheactofbreakingdownandfurtherdefiningProductBacklogitemsintosmallermorepreciseitems.Thisisanongoingactivitytoadddetails,suchasadescription,order,andsize.Attributesoftenvarywiththedomainofwork. TheDeveloperswhowillbedoingtheworkareresponsibleforthesizing.TheProductOwnermayinfluencetheDevelopersbyhelpingthemunderstandandselecttrade-offs. Commitment:ProductGoal TheProductGoaldescribesafuturestateoftheproductwhichcanserveasatargetfortheScrumTeamtoplanagainst.TheProductGoalisintheProductBacklog.TherestoftheProductBacklogemergestodefine“what”willfulfilltheProductGoal. Aproductisavehicletodelivervalue.Ithasaclearboundary,knownstakeholders,well-definedusersorcustomers.Aproductcouldbeaservice,aphysicalproduct,orsomethingmoreabstract. TheProductGoalisthelong-termobjectivefortheScrumTeam.Theymustfulfill(orabandon)oneobjectivebeforetakingonthenext. SprintBacklog TheSprintBacklogiscomposedoftheSprintGoal(why),thesetofProductBacklogitemsselectedfortheSprint(what),aswellasanactionableplanfordeliveringtheIncrement(how). TheSprintBacklogisaplanbyandfortheDevelopers.Itisahighlyvisible,real-timepictureoftheworkthattheDevelopersplantoaccomplishduringtheSprintinordertoachievetheSprintGoal.Consequently,theSprintBacklogisupdatedthroughouttheSprintasmoreislearned.ItshouldhaveenoughdetailthattheycaninspecttheirprogressintheDailyScrum. Commitment:SprintGoal TheSprintGoalisthesingleobjectivefortheSprint.AlthoughtheSprintGoalisacommitmentbytheDevelopers,itprovidesflexibilityintermsoftheexactworkneededtoachieveit.TheSprintGoalalsocreatescoherenceandfocus,encouragingtheScrumTeamtoworktogetherratherthanonseparateinitiatives. TheSprintGoaliscreatedduringtheSprintPlanningeventandthenaddedtotheSprintBacklog.AstheDevelopersworkduringtheSprint,theykeeptheSprintGoalinmind.Iftheworkturnsouttobedifferentthantheyexpected,theycollaboratewiththeProductOwnertonegotiatethescopeoftheSprintBacklogwithintheSprintwithoutaffectingtheSprintGoal. Increment AnIncrementisaconcretesteppingstonetowardtheProductGoal.EachIncrementisadditivetoallpriorIncrementsandthoroughlyverified,ensuringthatallIncrementsworktogether.Inordertoprovidevalue,theIncrementmustbeusable. MultipleIncrementsmaybecreatedwithinaSprint.ThesumoftheIncrementsispresentedattheSprintReviewthussupportingempiricism.However,anIncrementmaybedeliveredtostakeholderspriortotheendoftheSprint.TheSprintReviewshouldneverbeconsideredagatetoreleasingvalue. WorkcannotbeconsideredpartofanIncrementunlessitmeetstheDefinitionofDone. Commitment:DefinitionofDone TheDefinitionofDoneisaformaldescriptionofthestateoftheIncrementwhenitmeetsthequalitymeasuresrequiredfortheproduct. ThemomentaProductBacklogitemmeetstheDefinitionofDone,anIncrementisborn. TheDefinitionofDonecreatestransparencybyprovidingeveryoneasharedunderstandingofwhatworkwascompletedaspartoftheIncrement.IfaProductBacklogitemdoesnotmeettheDefinitionofDone,itcannotbereleasedorevenpresentedattheSprintReview.Instead,itreturnstotheProductBacklogforfutureconsideration. IftheDefinitionofDoneforanincrementispartofthestandardsoftheorganization,allScrumTeamsmustfollowitasaminimum.Ifitisnotanorganizationalstandard,theScrumTeammustcreateaDefinitionofDoneappropriatefortheproduct. TheDevelopersarerequiredtoconformtotheDefinitionofDone.IftherearemultipleScrumTeamsworkingtogetheronaproduct,theymustmutuallydefineandcomplywiththesameDefinitionofDone. EndNote ScrumisfreeandofferedinthisGuide.TheScrumframework,asoutlinedherein,isimmutable.WhileimplementingonlypartsofScrumispossible,theresultisnotScrum.Scrumexistsonlyinitsentiretyandfunctionswellasacontainerforothertechniques,methodologies,andpractices. Acknowledgements People OfthethousandsofpeoplewhohavecontributedtoScrum,weshouldsingleoutthosewhowereinstrumentalatthestart:JeffSutherlandworkedwithJeffMcKennaandJohnScumniotales,andKenSchwaberworkedwithMikeSmithandChrisMartin,andallofthemworkedtogether.ManyotherscontributedintheensuingyearsandwithouttheirhelpScrumwouldnotberefinedasitistoday. ScrumGuideHistory KenSchwaberandJeffSutherlandfirstco-presentedScrumattheOOPSLAConferencein1995.ItessentiallydocumentedthelearningthatKenandJeffgainedoverthepreviousfewyearsandmadepublicthefirstformaldefinitionofScrum. TheScrumGuidedocumentsScrumasdeveloped,evolved,andsustainedfor30-plusyearsbyJeffSutherlandandKenSchwaber.Othersourcesprovidepatterns,processes,andinsightsthatcomplementtheScrumframework.Thesemayincreaseproductivity,value,creativity,andsatisfactionwiththeresults. ThecompletehistoryofScrumisdescribedelsewhere.Tohonorthefirstplaceswhereitwastriedandproven,werecognizeIndividualInc.,Newspage,FidelityInvestments,andIDX(nowGEMedical). ©2020KenSchwaberandJeffSutherlandThispublicationisofferedforlicenseundertheAttributionShare-AlikelicenseofCreativeCommons,accessibleat https://creativecommons.org/licenses/by-sa/4.0/legalcode andalsodescribedinsummaryformat https://creativecommons.org/licenses/by-sa/4.0/.ByutilizingthisScrumGuide,youacknowledgeandagreethatyouhavereadandagreetobeboundbythetermsoftheAttributionShare-AlikelicenseofCreativeCommons. Memberships