Immunological memory is the phenomenon whereby B and T cells have the unique ability to respond with heightened kinetics and efficacy to subsequent encounter with Ag relative to the initial exposure. in this review, we examine recent developments in the phenotypic characterisation. of memory B cells, with an emphasis on the definition and functional properties of memory B-cell subsets in humans. Gene expression differences are also considered in light of the unique functional and survival properties of memory B cells, and mutations that alter memory formation and function are also examined. Finally, we consider recent advances in the understanding of germinal center B-cell differentiation through analysis of transcription factor networks operating in these B cells.