Ibrutinib is a novel oral tyrosine kinase inhibitor that irreversibly binds and inhibits tyrosine-protein kinase BTK (Bruton tyrosine kinase). BTK has been found to be important in the function of B-cell receptor signaling and therefore in the maintenance and expansion of various B-cell malignancies including chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). Targeting BTK with ibrutinib has been found to be an effective strategy in treating these malignancies. Phase I clinical testing in non-Hodgkin's lymphomas and CLL showed that the drug was extremely well tolerated with no major dose-limiting toxicities and a 54% overall response rate. Subsequently, two phase Ib/II studies were performed on patients with CLL, one in relapsed/refractory CLL and one in previously untreated elderly patients with CLL. Both of these studies continued to show good tolerability of the drug and an overall response rate of about 71% with extended duration of response. Another phase II study using ibrutinib in relapsed/refractory MCL was conducted and also showed that it was well tolerated with an overall response rate of 68% and extended duration of response. Due to these results, the U.S. Food and Drug Administration granted accelerated approval for ibrutinib in November 2013 for patients with MCL who had received at least one prior therapy and in February 2014 for patients with CLL who had received at least one prior therapy. This review will discuss the preclinical pharmacology, pharmacokinetics and clinical efficacy to date of ibrutinib in the treatment of CLL and MCL.