TheBlymphocytelineagerepresentsaleadingsystemforexploring- lecularmechanismsthatunderliecellfatespecification, differentiationand cellular activation. In the past five years major advances have been achievedintheanalysisofearlyBcelldevelopment, AIDdependentclass switchrecombinationaswellassomatichypermutationandBlimp-1re- latedplasmacelldifferentiation. Manyofthesefindingsandtheirimpli- tionsarecoveredinthisvolume. Twoemergentareasofresearchthatare includedinthecontributionsfocusonthepre-BCRandIkaros-familyp- teins. Thepre-BCRisanunusualmoleculardevicethatisusedtoexecute...