This article focuses on the functions of NF-kappaB that vitally impact lymphocytes and thus adaptive immunity. NF-kappaB has long been known to be essential for many of the responses of mature lymphocytes to invading pathogens. In addition, NF-kappaB has important functions in shaping the immune system so it is able to generate adaptive responses to pathogens. In both contexts, NF-kappaB executes critical cell-autonomous functions within lymphocytes as well as within supportive cells, such as antigen-presenting cells or epithelial cells. It is these aspects of NF-kappaB's physiologic impact that we address in this article.