The generation and maintenance of B lymphocytes is controlled by biochemical signals tramsitted by the B cell antigen receptor (BCR) complex. These signals are transduced by multiple cytoplasmic protein tyrosine kinases (PTKs) including Lyn, Syk, and Bruton's tyrosine kinase (BTK). Upon BCR engagement, these PTKs activate downstream effectors, including transcription factors that modulate gene expression. In turn activation of down stream effectors is critical for B cell survival, cell cycle progression, and antibody production. Our studies focus on the role of BTK in these biological responses. We have discovered that BTK is required for activation of the BCR-responsive transcription factor, NF-κB. Furthermore, BTK-dependent activation of NF-κB isessential for reprogramming the expression of genes that control B cell survival and proliferation. The biochemical mechanisms by which BTK regulates signaling components that activate NF-κB, and the identification of BTK-responsive genes are under investigation. Elucidation of these regulatory mechanisms is expected to reveal new therapeutic targets for B cell pathologies involving defects in BTK, including X-linked agammaglobulinemia (XLA).