The B cell antigen receptor (BCR) and its downstream pathways are pivotal in the 
pathogenesis of chronic lymphocytic leukemia (CLL). Recently, inhibitors of 
kinases in the BCR pathway have shown promising clinical activity in CLL. Based 
upon these results, the treatment paradigm for CLL will likely undergo major 
changes. The kinases essential for BCR signal transduction, which are emerging 
as targets for CLL treatment, and the specific inhibitors under development are 
the focus of this chapter. In particular, the BTK inhibitor ibrutinib and the 
PI3K inhibitor idelalisib (GS-1101) are two evolving targeted therapies with the 
most mature clinical data.