The pharmacology, pharmacokinetics, pharmacodynamics, clinical efficacy, and safety of ibrutinib are described.Ibrutinib is a first-in-class oral inhibitor of Bruton tyrosine kinase (BTK) approved for treatment of relapsed chronic lymphocytic leukemia (CLL). Ibrutinib blocks downstream signaling of the B-cell receptor, disrupting stromal microenvironment interactions and B-cell cytokine signaling. BTK inhibition has been shown to be effective in relapsed or refractory CLL. A recent Phase III study evaluated ibrutinib (420 mg daily) versus ofatumumab (consistent with labeling) in relapsed or refractory CLL with a primary endpoint of progression free survival (PFS, n = 391). After a median follow-up period of 9.4 months, a PFS was not attained in ibrutinib-treated individuals with and without deletion 17p. In contrast, ofatumumab-treated individuals experienced a PFS of 8.1 months and those with deletion 17p experienced a PFS of 5.8 months. Major hemorrhage was reported in 2 (1%) patients treated with ibrutinib, and a total of 8 (4%) patients discontinued treatment due to toxicity or adverse reactions. Partial response or partial response with lymphocytosis was achieved in 63% of ibrutinib-treated individuals as determined by independent assessments. Overall, ibrutinib reduced the rate of mortality by 57%.Ibrutinib is a first-in-class, orally active, irreversible BTK inhibitor with a novel mechanism of action. This unique mechanism of action and high overall response rates observed in clinical trials make ibrutinib an attractive second-line option in patients who have disease progression while receiving monoclonal antibody therapy or chemoimmunotherapy.