The Rel/nuclear factor (NF)-kappaB family of transcription factors have been implicated in the regulation of a wide variety of genes, in particular those encoding proteins crucial to the function of the immune system. Through the use of mutant mice that lack one or more of these proteins, we have begun to examine the individual and combined roles of Rel, RelA and NF-kappaB1 in B-cell development and function. Here we outline and discuss how these transcription factors operate as differentiation stage-specific regulators of B-cell development, survival, division and immunoglobulin expression, emphasizing those Rel/NF-kappaB-regulated genes that mediate these functions.